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phenotypes

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observable characteristics. affected by environmental influences.

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genotype

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the complex bled of genetic information that determines our species and influences all our unique characteristics.

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chromosomes

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rodlike structures which store and transmit genetic information. 23 matching pairs in humans, XY male XX female.

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chromosomes are made up of

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DNA, a long double stranded molecule that looks like a twisted ladder. Each rung of the ladder consists of a pair of chemical substances called bases.

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gene

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a segment of DNA along the length of the chromosome. Genes can be different lengths.

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a unique feature of human DNA is that it can duplicate itself through a process called

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mitosis.

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proteins

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trigger chemical reactions and are the biological foundations on which our characteristics are built.

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within the cell, a wide variety of

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environmental factors modify gene expression. So even at this microscopic level, biological events modify gene expression.

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gametes

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sex cells, sperm and ovum. formed through meiosis, which halves the number of chromosomes normally present.

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when sperm and ovum unite, you have a

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zygote.

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crossing over

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chromosomes next to each other break at one or more points along their length and exchange segments, so that genes from one are replaced by genes from another. This shuffling of genes creates new hereditary combinations.

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meiosis is adaptive

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because it generates offspring that vary in phenotype, it increases the chances that at least some members of a species will cope with ever changing environments and survive.

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how many sperm/ovum produced?

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4 sperm, 1 ovum.

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autosomes

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not sex chromosomes. 22 pairs, arranged from longest (1) to shortest (22)

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the 23rd pair of chromosomes are the

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sex chromosomes. XY in male, XX in female.

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identical or monozygotic twins

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they have the same genetic makeup. A zygote that has started to duplicate separates into two clusters of cells that result in two individuals.

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fraternal or dizygotic twins

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the most common type of multiple birth, result from the release and fertilization of two ova. No more alike than ordinary siblings.

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allele

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Each form of a gene. Two forms of each gene occur at the same place on the chromosome, one from the mother and the other from the father.

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homozygous

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if the alleles from both parents are alike

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heterozygous

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if the alleles differ.

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relationships between alleles determine

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phenotypes

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dominant-recessive inheritance

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happens in many heterozygous pairings. Only one allele affects the child's characteristics, its called dominant. The other has no effect, its called recessive.

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carrier

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heterozygous (Xx), carry both alleles and can pass both down to offspring.

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phenylketonuria (PKU)

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one of the most frequently occurring recessive disorders, affects the way the body break down proteins in many foods. Infants born with two recessive alleles lack an enzyme that converts one of the basic amino acids (Phenylalanine) into a byproduct essential for body functioning (tyrosine). Can cause damage to central nervous system. Alters pigmentation, children with this usually have blonde hair and blue eyes.

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modifier genes

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enhance or dilute the effects of other genes.

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incomplete dominance

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a pattern of inheritance in which both alleles are expressed in the phenotype, resulting in a combined trait or one that is intermediate between the two. EX: sickle cell anemia. Hetero carriers are usually normal but when in less oxygen rich areas, the recessive allele shows itself -carrier are resistant to malaria

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x linked inheritance

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when theres a harmful allele on the x chromosome. males are more likley to be affected because their sec chromosomes dont match. (also Y chromosome is much shorter and lacks many corresponding allesls to override) -an example is hemophelia

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genomic imprinting

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alleles are imprinted, or chemically marked, so that one pair member (either mothers or fathers) is activated, regardless of its makeup. -helps us to understand certain puzzling genetic patterns. people with diabetes tend to have fathers who have it, and people with asthma tend to have mothers who have it. -can operate on the sex chromosome as fragile x syndrome, the most common inherited cause of mental retardation. expressed only when an abnormal gene is passed from mother to child. these are more common in males.-

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mutation

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a sudden but permanent change in a segment of DNA

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germ-line mutation

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which takes place in the cells that give rise to gametes

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somatic mutation

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normal body cells that mutate, can happen at any part of life.

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polygenic inheritance

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many genes are determine the characteristic in question.

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many chromosomal defects result from

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mistakes occurring during meiosis, when the ovum and sperm are formed.

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down syndrome

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the most common chromosomal disorder. Results from a failure of the 21st pair of chromosomes to separate during meiosis, so the new individual inherits 3 of these instead of the normal 2. AKA trisomy 21. -in other cases and extra 21st chromosome is attached to part of another chromosome, called translocation pattern. -or an error occurs during the early stages of mitosis , causing some but not all the body cells so have the defective chromosome (mosaic pattern)

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consequences of down syndrome

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-mental retardation, memory and speech problems, limited vocabulary, slow motor development. reduction in size of brain. short, stocky build, flattened face, protruding tounge, almond shaped eyes, (50%) unusual crease running across palm of hand. -born with eye cataracts, hearing loss and heart and intestinal defects. -when they grow older, show signs of dementia

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infants of down syndrome

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-smile less readily -poor eye to eye contact -weak muscle tone -explore objects less persistently

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genetic counseling

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a communication process designed to help couples asses their chances of giving birth to a baby with a hereditary disorder and choose the best course of action in view of risks and family goals.

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pedigree

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picture of the family tree in which affected relatives (of genetic disorders) are identified.

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prenatal diagnostic method

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medical procedures that permit detection of developmental problems before birth

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women of advanced marital age are prime candidates for

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amniocentesis or chronic villus sampling

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human genome project

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an ambitious international research program aimed at deciphering the chemical make up of human genetic material . They are identifying all genes and their functions, including protein products and what these products do

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gene therapy

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correcting genetic abnormalities by delivering DNA carrying a functional gene to the cell

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corpus luteum

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secretes hormones that prepare the lining of the uterus to receive a fertilized ovum. if pregnancy does not occur, the corpus luteum shrinks, and the uterus lining is discarded two weeks later

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the 38 week period of pregnancy is divided into 3 period

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1) the period of the zygote 2)the period of the embryo 3)the period of the fetus

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period of the zygote

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lasts about 2 weeks, from fertilization until the tin mss of cells drift down and out of the fallopian tube and attaches itself to the wall of the uterus.

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blastocyst

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60 to 70 cells exist that form a hollow, fluid-filled ball called a blastocyst.

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the embryonic disk

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the cells on the inside of the blastocyst, will become the new organism.

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trophoblast

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the thin outer ring of the blastocyst, will become the structures that provide covering and nourishment.

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Implantation occurs

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Between the seventh and ninth days. The blastocyst burrows deep into the uterine lining where, surrounded by the woman's nourishing blood, it starts to grow in earnest.

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At first, the trophoblast (protective outer layer)

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multiplies fastest. It forms a membrane, called the amnion, that encloses the developing organism in amniotic fluid, which helps keep the temperature of the prenatal world constant and provides a cushion against any jolts caused by the woman's movement. A yolk sac emerges that produces blood cells until the developing liver, spleen, and bone marrow are mature enough to take over this function

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By the end of the second week, cells of the trophoblast form another protective membrane

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the chorion, which surrounds the amnion. From the chorion, tiny fingerlike villi, or blood vessels, emerge. As these villi burrow into the uterine wall, a special organ called the placenta starts to develop.

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the placenta

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By bringing the mother's and the embryo's blood close together, the placenta permits food and oxygen to reach the developing organism and waste products to be carried away.

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the umbilical cord

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The placenta is connected to the developing organism by the umbilical cord, which first appears as a primitive body stalk and, during the course of pregnancy, grows to a length of 1 to 3 feet. The umbilical cord contains one large vein that delivers blood loaded with nutrients and two arteries that remove waste products

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The period of the embryo lasts from

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implantation through the eighth week of pregnancy. During these brief six weeks, the most rapid prenatal changes take place, as the groundwork is laid for all body structures and internal organs.

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In the first week of the embryonic period

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the embryonic disk forms three layers of cells: (1) the ectoderm, which will become the nervous system and skin; (2) the mesoderm, from which will develop the muscles, skeleton, circulatory system, and other internal organs; (3) the endoderm, which will become the digestive system, lungs, urinary tract, and glands. These three layers give rise to all parts of the body.

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the ___ forms the fastes

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nervous system develops fastest. The ectoderm folds over to form the neural tube, or primitive spinal cord.

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While the nervous system is developing

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While the nervous system is developing, the heart begins to pump blood, and muscles, backbone, ribs, and digestive tract appear.

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While the nervous system is developing, the heart begins to pump blood, and muscles, backbone, ribs, and digestive tract appear. At the end of the first month

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—only 1?4 inch long—consists of millions of organized groups of cells with specific functions.

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In the second month

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growth continues rapidly. -eyes, ears, nose, jaw, and neck form. -Tiny buds become arms, legs, fingers, and toes. -The intestines grow, the heart develops separate chambers, and the liver and spleen take over production of blood cells so that the yolk sac is no longer needed. -Changing body pro- portions cause the embryo's posture to become more upright.

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At 7 weeks, production of

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neurons (nerve cells that store and transmit information) begins deep inside the neural tube. Once formed, neurons begin traveling along tiny threads to their permanent locations, where they will form the major parts of the brain.

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At the end of this period, the embryo

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—about 1 inch long and 1?7 ounce in weight—can already sense its world. It responds to touch, particularly in the mouth area and on the soles of the feet. And it can move, although its tiny flutters are still too light to be felt by the mother

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The period of the fetus

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from the ninth week to the end of pregnancy, is the longest prenatal period. During this "growth and finishing" phase, the organism increases rapidly in size, especially from the ninth to the twentieth week.

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In the third month,

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-the organs, muscles, and nervous system start to become organized and connected. When the brain signals, the fetus kicks, bends its arms, forms a fist, curls its toes, turns its head, opens its mouth, and even sucks its thumb, stretches, and yawns. -Body position changes occur as often. -tiny lungs begin to expand and contract. By the twelfth week, the external genitals are well-formed, and the sex of the fetus can be detected with ultrasound (Sadler, 2009). Other finishing touches appear, such as fingernails, toenails, tooth buds, and eyelids. The heartbeat can now be heard through a stethoscope. Prenatal development is sometimes divided into trimes- ters, or three equal time periods. At the end of the third month, the first trimester is complete.

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By the twelfth week

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the external genitals are well-formed, and the sex of the fetus can be detected with ultrasound. -Other finishing touches appear, such as fingernails, toenails, tooth buds, and eyelids. The heartbeat can now be heard through a stethoscope.

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Prenatal development is sometimes divided into

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trimesters, or three equal time periods. At the end of the third month, the first trimester is complete.

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By the middle of the second trimester

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between 17 and 20 weeks, the new being has grown large enough that the mother can feel its movements.

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A white, cheeselike substance called

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vernix covers the skin, protecting it from chapping during the long months spent in the amniotic fluid. White, downy hair called lanugo also covers the entire body, helping the vernix stick to the skin.

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At the end of the second trimester

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many organs are well-developed. Also, most of the brain's billions of neurons are in place; few will be produced after this time. However, glial cells, which support and feed the neurons, continue to increase rapidly throughout the remaining months of pregnancy, as well as after birth.

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Consequently, brain weight

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increases tenfold from the twentieth week until birth. At the same time, neurons begin forming synapses, or connections, at a rapid pace.

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Brain growth means

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New behavioral capacities. The 20-week-old fetus can be stimulated as well as irritated by sounds. Slow eye movements appear, with rapid eye movements at 22 weeks. -fetuses try to shield their eyes from the light with their hands, indicating that sight has begun to emerge. Still, a fetus born at this time cannot survive. Its lungs are too immature, and the brain cannot yet control breathing movements or body temperature.

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During the final trimester

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a fetus born early has a chance of survival.

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The point at which the baby can first survive

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called the age of viability, occurs some- time between 22 and 26 weeks

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A baby born between the seventh and eighth months, .

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usually needs oxygen assistance to breathe. Although the brain's respiratory center is now mature, tiny air sacs in the lungs are not yet ready to inflate and exchange carbon dioxide for oxygen.

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During the 3rd trimester, the brain

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continues to make great strides. The cerebral cortex, the seat of human intelligence, enlarges. -Convolutions and grooves in its surface appear, permitting a dramatic increase in surface area that allows for maximum prenatal brain growth without the full- term baby's head becoming too large to pass through the birth canal.

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During the 3rd trimester, as neural connectivity and organization improve

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fetal heart rate reveals no periods of alertness. Between 30 and 34 weeks, fetuses show rhythmic alternations between sleep and wakefulness that gradually increase in organization.

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Gradual wakefulness in the fetus

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leads to synchrony between fetal heart rate and motor activity peaks: A rise in heart rate is usually followed within 5 seconds by a burst of motor activity. These are clear signs that coordinated neural networks are beginning to form in the brain.

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By the end of pregnancy, the fetus takes on

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the beginnings of a personality. Higher fetal activity in the last weeks of pregnancy predicts a more active infant in the first month of life—a relationship that, for boys, persists into early childhood.

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The third trimester also brings greater

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responsiveness to external stimulation. Between 23 and 30 weeks, connections form between the cerebral cortex and brain regions involved in pain sensitivity. By this time, painkillers should be used in any surgical procedures

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Around 28 weeks, fetuses .. and at 30 weeks

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blink their eyes in reaction to nearby sounds. -fetuses presented with a repeated auditory stimulus against the mother's abdomen initially react with a rise in heart rate and body movements.

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over the next 6 weeks (week 30 onward)

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fetuses distinguish the tone and rhythm of different voices and sounds: They show systematic heart rate changes in response to a male versus a female speaker, to the mother's voice versus a stranger's, to a stranger speaking their native language (English) versus a foreign language (Mandarin Chinese), and to a simple familiar melody (descending tones) versus an unfamiliar melody (ascending tones). they can even hear stories in the womb

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In the final three months, the fetus

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gains more than 5 pounds and grows 7 inches. As it fills the uterus, it gradually moves less often. In addition, brain development, which enables the organism to inhibit behavior, contributes to this decline in physical activity.

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In the eighth month

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a layer of fat is added to assist with temperature regulation. The fetus also receives antibodies from the mother's blood to protect against illnesses, since the newborn's own immune system will not work well until several months after birth.

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In the last weeks

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most fetuses assume an upside-down position, partly because of the shape of the uterus and also because the head is heavier than the feet. Growth slows, and birth is about to take place.

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The term teratogen refers to

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any environmental agent that causes damage during the pre- natal period

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Teratogens It depends on the following factors (4)

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? Dose. As we discuss particular teratogens, you will see that larger doses over longer time periods usually have more negative effects. ? Heredity. The genetic makeup of the mother and the developing organism plays an important role. Some individuals are better able than others to withstand harmful environments. ? Other negative influences. The presence of several negative factors at once, such as additional teratogens, poor nutrition, and lack of medical care, can worsen the impact of a single harmful agent. ? Age. The effects of teratogens vary with the age of the organism at time of exposure. To understand this last idea, think of the sensitive period concept. Recall that a sensitive period is a limited time span in which a part of the body or a behavior is biologically prepared to develop rapidly. During that time, it is especially sensitive to its surroundings. If the environment is harmful, then damage occurs, and recovery is difficult and sometimes impossible.

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In the period of the zygote, before implantation, teratogens

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rarely have any impact. If they do, the tiny mass of cells is usually so damaged that it dies. The embryonic period is the time when serious defects are most likely to occur because the foundations for all body parts are being laid down. During the fetal period, tera- togenic damage is usually minor. However, organs such as the brain, ears, eyes, teeth, and genitals can still be strongly affected.

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(teratogens) The embryonic period is the time when

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serious defects are most likely to occur because the foundations for all body parts are being laid down. .

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(teratogens)During the fetal period

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teratogenic damage is usually minor. However, organs such as the brain, ears, eyes, teeth, and genitals can still be strongly affected.

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The effects of teratogens

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go beyond immediate physical damage. Some health outcomes are delayed and may not show up for decades. Furthermore, psychological consequences may occur indirectly, as a result of physical damage.

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thalidomide

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(early 1960s) thalidomide was widely available. When taken by mothers 4 to 6 weeks after conception, thalidomide produced gross deformities of the embryo's developing arms and legs and, less frequently, damage to the ears, heart, kidneys, and genitals. -As children exposed to thalidomide grew older, many scored below average in intelligence.

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diethylstilbestrol (DES)

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a synthetic hormone. was widely prescribed between 1945 and 1970 to prevent miscarriages. - As daughters of these mothers reached adolescence and young adulthood, they showed unusually high rates of cancer of the vagina, malformations of the uterus, and infertility. -When they tried to have children, their pregnancies more often resulted in prematurity, low birth weight, and miscarriage than those of non-DES-exposed women. Young men showed an increased risk of genital abnormalities and cancer of the testes.

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Accutane

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Currently, the most widely used potent teratogen is a vitamin A derivative (known by the generic name isotretinoin). Prescribed to treat severe acne and taken by hundreds of thousands of women of childbearing age in industrialized nations. Exposure during the first trimester of pregnancy results in eye, ear, skull, brain, heart, and immune system abnormalities -Accutane's packaging warns users to avoid pregnancy by using two methods of birth control, but many women do not heed this advice

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Babies born to users of cocaine, heroin, or methadone (a less addictive drug used to wean people away from heroin)

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are at risk for a wide variety of problems, including prematurity, low birth weight, physical defects, breathing difficulties, and death at or around the time of birth. In addition, these infants are born drug-addicted. They are often feverish and irritable and have trouble sleeping, and their cries are abnormally shrill and piercing—a common symptom among stressed newborns.

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Throughout the first year, heroin- and methadone-exposed infants are

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less attentive to the environment than non-exposed babies, and their motor development is slow. After infancy, some children get better, whereas others remain jittery and inattentive. The kind of parenting they receive may explain why difficulties continue for some but not for others

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Evidence on cocaine suggests that some prenatally exposed babies

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develop lasting problems. Cocaine constricts the blood vessels, causing oxygen delivery to the developing organism to fall for 15 minutes following a high dose. -It also can alter the production and functioning of neurons and the chemical balance in the fetus's brain.

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with cocaine, Several studies report

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-perceptual, motor, attention, memory, language, and impulse- control problems that persist into the preschool and school years. And compared to non-exposed infants, cocaine-exposed babies show greater stress reactivity, as indicated by a more rapid rise in saliva concentrations of cortisol to emotionally arousing events. - By school age, children with a history of prenatal cocaine exposure display a reduced cortisol response during stressful mental activity.Recall from Chapter 2 that cortisol levels that are either too high or too low signal a disrupted stress response system—a risk factor for illness and learning and behavior problems -Other investigations, however, report no major negative effects of prenatal cocaine exposure (Behnke et al., 2006; Frank et al., 2005; Hurt et al., 2009). These contradictory find- ings indicate how difficult it is to isolate the precise damage caused by illegal drugs.

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marijuana

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Researchers have linked prenatal marijuana exposure to smaller head size (a measure of brain growth); to attention, memory, and academic achievement difficulties; to impulsivity and overactivity; and to depression as well as anger and aggression in childhood and adolescence. -- As with cocaine, however, lasting consequences are not well-established.

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tobacco

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-The best-known effect of smoking during the prenatal period is low birth weight. But the likelihood of other serious consequences, such as miscarriage, prematurity, cleft lip and palate, impaired heart rate and breathing during sleep, infant death, and asthma and cancer later in childhood, also increases. (even passive smoking can result in this)

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The more cigarettes a mother smokes,

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the greater the chances that her baby will be affected. And if a pregnant woman stops smoking at any time, even during the third trimester, she reduces the likelihood that her infant will be born underweight and suffer from future problems

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Newborns of smoking mothers are

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less attentive to sounds, display more muscle tension, are more excitable when touched and visually stimulated, and more often have colic (persistent crying)—findings that suggest subtle negative effects on brain development. -Consistent with this view, prenatally exposed youngsters tend to have shorter attention spans, difficulties with impulsivity and overactivity, poorer memories, lower mental test scores, and higher levels of disruptive,

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Exactly how can smoking harm the fetus?

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Nicotine, the addictive substance in tobacco, constricts blood vessels, lessens blood flow to the uterus, and causes the placenta to grow abnormally. This reduces the transfer of nutrients, so the fetus gains weight poorly. Also, nicotine raises the concentration of carbon monoxide in the bloodstreams of both mother and fetus. Carbon monoxide displaces oxygen from red blood cells, damaging the central nervous system and slowing body growth in the fetuses of laboratory animals

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fetal alcohol spectrum disorder (FASD)

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a term that encompasses a range of physical, mental, and behavioral outcomes caused by pre-natal alcohol exposure

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Fetal alcohol syndrome (FAS), distinguished by

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(a) slow physical growth, (b) a pattern of three facial abnormalities (short eyelid openings; a thin upper lip; a smooth or flattened philtrum, or indentation running from the bottom of the nose to the center of the upper lip), and (c) brain injury, evident in a small head and impairment in at least three areas of functioning—for example, memory, language and communication, attention span and activity level (overactivity), planning and reasoning, motor coordination, or social skills.

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Partial fetal alcohol syndrome (p-FAS)

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characterized by (a) two of the three facial abnormalities just mentioned and (b) brain injury, again evident in at least three areas of impaired functioning. Mothers of children with p-FAS generally drank alcohol in smaller quantities, and children's defects vary with the timing and length of alcohol exposure.

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Alcohol-related neurodevelopmental disorder (ARND)

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in which at least three areas of mental functioning are impaired, despite typical physical growth and absence of facial abnormalities. Again, prenatal alcohol exposure, though confirmed, is less pervasive than in FAS

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Even when provided with enriched diets, FAS babies

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fail to catch up in physical size during infancy or childhood. Mental impairment associated with all three FASD diagnoses is also permanent:

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The more alcohol a woman consumes during pregnancy,

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poorer the child's motor coordination, speed of information processing, attention, memory, reasoning, and intelligence and achievement test scores during the preschool and school years .

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In adolescence and early adulthood, FASD is associated with

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persisting attention and motor-coordination deficits, poor school performance, trouble with the law, inappropriate social and sexual behaviors, alcohol and drug abuse, and lasting mental health problems, including high stress reactivity and depression

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How does alcohol produce its devastating effects?

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-First, it interferes with production and migration of neurons in the primitive neural tube. EEG and fMRI research reveals reduced brain size, damage to many brain structures, and abnormalities in brain functioning, including the electrical and chemical activity involved in transferring messages from one part of the brain to another. -Second, the body uses large quantities of oxygen to metabolize alcohol. A pregnant woman's heavy drinking draws away oxygen that the developing organism needs for cell growth.

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After each disaster (radiation)

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the incidence of miscarriage and of babies born with underdeveloped brains, physical deformities, and slow physical growth rose dramatically

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Even when a radiation-exposed baby seems normal,

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problems may appear later. For example, even low-level radiation, as the result of industrial leakage or medical X-rays, can increase the risk of childhood cancer

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many babies are "born polluted" by chemicals that

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not only impair prenatal development but also increase the chances of health problems and life-threatening diseases later on. Prenatal exposure to traffic-related air pollution due to residence near roadways, for example, is linked to lower birth weight, with complicated pregnancies at greater risk

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mercury

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Many children born at the time displayed physical deformities, mental retardation, abnormal speech, difficulty in chewing and swallowing, and uncoordinated movements. High levels of prenatal mercury exposure disrupt production and migration of neurons, causing widespread brain damage.

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Prenatal mercury exposure from maternal seafood diets, assessed by measuring mercury concentration in umbilical-cord blood and tissue, predicts

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deficits in speed of cognitive processing and motor, attention, and verbal test performance during the school years. Pregnant women are wise to avoid eating long-lived predatory fish, including swordfish, albacore tuna, and shark, which are heavily contaminated with mercury.

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polychlorinated biphenyls (PCBs)

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were used to insulate electrical equipment, until research showed that, like mercury, they found their way into waterways and entered the food supply. -prenatal exposure to very high levels of PCBs in rice oil resulted in low birth weight, discolored skin, deformities of the gums and nails, EEG brain- wave abnormalities, and delayed cognitive development Steady, low-level PCB exposure is also harmful. Women who frequently ate PCB- contaminated fish, compared with those who ate little or no fish, had infants with lower birth weights, smaller heads, greater stress reactivity, persisting attention and memory difficulties, and lower intelligence test scores in childhood

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Another teratogen, lead,

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,is present in paint flaking off the walls of old buildings and in certain materials used in industrial occupations. High levels of prenatal lead exposure are consistently related to prematurity, low birth weight, brain damage, and a wide variety of physical defects. Even at low levels, affected infants and children show slightly poorer mental and motor development. The greater the prenatal lead exposure, the lower children's test scores.

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Finally, prenatal exposure to dioxins—toxic compounds resulting from incineration

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-is linked to brain, immune system, and thyroid damage in babies and to an increased incidence of breast and uterine cancers in women, perhaps through altering hormone levels. Furthermore, even tiny amounts of dioxin in the paternal blood stream cause a dramatic change in the sex ratio of offspring: Affected men father nearly twice as many girls as boys. Dioxin seems to impair the fertility of Y-bearing sperm prior to conception.

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Consistent with the sensitive-period concept, the greatest damage occurs when rubella strikes during the

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embryonic period. More than 50 percent of infants whose mothers become ill during that time show deafness; eye deformities, including cataracts; heart, genital, urinary, intestinal, bone, and dental defects; and mental retardation. Infection during the fetal period is less harmful, but low birth weight, hearing loss, and bone defects may still occur. The organ damage inflicted by prenatal rubella often leads to lifelong health problems, including severe mental illness (especially schizophrenia), diabetes, cardio- vascular disease, and thyroid and immune-system dysfunction in adulthood. Routine vaccination in infancy and childhood has made new rubella out- breaks unlikely in industrialized nations. But an estimated 100,000 cases of prenatal infection continue to occur each year, primarily in developing countries in Africa and Asia with weak or absent immunization programs.

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The human immunodeficiency virus (HIV)

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-which can lead to acquired immune deficiency syndrome (AIDS), a disease that destroys the immune system, has infected increasing numbers of women over the past two decades.

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AIDS progresses

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rapidly in infants. By 6 months, weight loss, diarrhea, and repeated respiratory illnesses are common. The virus also causes brain damage, as indicated by seizures, gradual loss in brain weight, and delayed mental and motor development. Nearly half of prenatal AIDS babies die by 1 year of age and 90 percent by age 3. Antiretroviral drug treatment reduces prenatal AIDS transmission by as much as 95 percent, with no harmful consequences of drug therapy for children. These medications have led to a dramatic decline in prenatally acquired AIDS in Western nations. Although distribution is increasing, antiretroviral drugs are still not widely available in impoverished regions of the world

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the developing organism is especially sensitive to the family of herpes viruses,

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-for which no vaccine or treatment exists. Among these, cytomegalovirus (the most frequent prenatal infection, transmitted through respiratory or sexual contact) and herpes simplex 2 (which is sexually transmitted) are especially dangerous. In both, the virus invades the mother's genital tract, infecting babies either during pregnancy or at birth. Both diseases often have no symptoms, very mild symptoms, or symptoms with which people are unfamiliar, thereby increasing the likelihood of contagion. Pregnant women who are not in a mutually monogamous relationship are at greatest risk.

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Bacterial and Parasitic Diseases: Among the most common is

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toxoplasmosis, caused by a parasite found in many animals. Pregnant women may become infected from eating raw or undercooked meat or from contact with the feces of infected cats. About 40 percent of women who have the disease transmit it to the developing organism. If it strikes during the first trimester, it is likely to cause eye and brain damage. Later infection is linked to mild visual and cognitive impairments. And about 80 percent of affected newborns with no obvious signs of damage develop learning or visual disabilities in later life. Expectant mothers can avoid toxoplasmosis by making sure that the meat they eat is well-cooked, having pet cats checked for the disease, and turning over care of litter boxes to other family members.

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Besides exposure to teratogens

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maternal exercise, nutrition, and emotional well-being affect the embryo and fetus

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In healthy, physically fit women, regular moderate exercise, such as walking, swimming, biking, or an aerobic workout, is related to

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increased birth weight and a reduction in risk for certain complications, such as pregnancy-induced maternal diabetes and high blood pressure. However, frequent, vigorous, extended exercise—working up a sweat for more than 30 minutes, four or five days a week, especially late in pregnancy—results in lower birth weight than in healthy, nonexercising controls. Hospital-sponsored childbirth education programs frequently offer exercise classes and suggest appropriate routines that help women prepare for labor and delivery. During the last trimester, when the abdomen grows very large, mothers have difficulty moving freely and often must cut back on exercise. Most women, however, do not engage in sufficient moderate exercise during pregnancy to promote their own and their baby's health. An expectant mother who remains fit experiences fewer physical discomforts, such as back pain, upward pressure on the chest, or difficulty breathing in the final weeks.

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During the prenatal period, when children are growing more rapidly than at any other time, they depend totally on the mother for nutrients. A healthy diet that results in a maternal weight gain of

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25 to 30 pounds (10 to 13.5 kilograms) helps ensure the health of mother and baby.

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the sensitive-period concept operates with nutrition, just as it does with teratogens. Women affected by the famine during the first trimester

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were more likely to have miscarriages or give birth to babies with physical defects. When women were past the first trimester, fetuses usually survived, but many were born underweight and had small heads

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Prenatal malnutrition can cause

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serious damage to the central nervous system. The poorer the mother's diet, the greater the loss in brain weight, especially if malnutrition occurred during the last trimester. During that time, the brain is increasing rapidly in size, and for it to reach its full potential, the mother must have a diet high in all the basic nutrients. An inadequate diet during pregnancy can also distort the structure of other organs, including the liver, kidneys, and pancreas, resulting in lifelong health problems, including cardiovascular disease and diabetes in adulthood.

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Because poor nutrition suppresses development of the immune system, prenatally malnourished babies

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frequently catch respiratory illnesses. In addition, they often are irritable and unresponsive to stimulation. Like drug-addicted newborns, they have a high-pitched cry that is particularly distressing to their caregivers. In poverty-stricken families, these effects quickly combine with a stressful home life. With age, low intelligence test scores and serious learning problems become more apparent.

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Many studies show that providing pregnant women with adequate food has

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a substantial impact on the health of their newborn babies. Yet the growth demands of the prenatal period require more than just increased quantity of food. Vitamin- mineral enrichment is also crucial.

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For example, taking a folic acid supplement around the time of conception

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reduces by more than 70 percent abnormalities of the neural tube, such as anencephaly and spina bifida. Folic acid supplementation early in pregnancy also reduces the risk of other physical defects, including cleft lip and palate, urinary tract abnormalities, and limb deformities. Furthermore, adequate folic acid intake during the last 10 weeks of pregnancy cuts in half the risk of premature delivery and low birth weight. Because of these findings, U.S. government guidelines recommend that all women of childbearing age consume 0.4 milligrams of folic acid per day. For women who have previously had a pregnancy affected by neural tube defect, the recommended amount is 4 or 5 milligrams. About half of U.S. pregnancies are unplanned, so government regulations mandate that bread, flour, rice, pasta, and other grain products be fortified with folic acid. mandatory grain fortification has resulted in substantial reductions in neural tube defects in the United States and other nations.

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Other vitamins and minerals also have established benefits. Enriching women's diets with calcium helps

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prevent maternal high blood pressure and premature births. Adequate magnesium and zinc reduce the risk of many prenatal and birth complications. Fortifying table salt with iodine virtually eradicates infantile hypothyroidism, a condition of stunted growth and cognitive impairment, caused by prenatal iodine deficiency—a common cause of mental retardation in many parts of the developing world.

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Sufficient vitamin C and iron beginning early in the pregnancy

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promote growth of the placenta and healthy birth weight. prenatal iron depletion as a result of maternal diabetes interferes with development of brain structures involved in memory, thereby impairing children's learning.

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Intense anxiety—especially during the first two trimesters—is associated with

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higher rates of miscarriage, prematurity, low birth weight, infant respiratory and digestive illnesses, colic (persistent infant crying), sleep dis- turbances, and irritability during the child's first three years

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How can maternal stress affect the developing organism?

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When we experience fear and anxiety, stimulant hormones released into our bloodstream cause us to be "poised for action." Large amounts of blood are sent to parts of the body involved in the defensive response—the brain, the heart, and muscles in the arms, legs, and trunk. Blood flow to other organs, including the uterus, is reduced. As a result, the fetus is deprived of a full supply of oxygen and nutrients.

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Excessive fetal stress may permanently alter

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neurological functioning as well, thereby heightening stress reactivity in later life. -infants and children of mothers who experienced severe prenatal anxiety displayed cortisol levels that were either abnormally high or abnormally low, both of which signal reduced physiological capacity to manage stress.

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Furthermore, maternal emotional stress during pregnancy predicts

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childhood anxiety, short attention span, anger, aggression, overactivity, and lower mental test scores, above and beyond the impact of other risks, such as maternal smoking during pregnancy, low birth weight, postnatal maternal anxiety, and low family income. - Enhancing supportive social networks for pregnant mothers can help prevent prenatal complications.

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Maternal stress hormones also cross the placenta

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causing a dramatic rise in fetal stress hormones (evident in the amniotic fluid) and in fetal heart rate, blood pressure, blood glucose, and activity level. These processes are believed to increase the lifelong risk of serious illnesses, such as cardiovascular disease and diabetes

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three stages of childbirth

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1. Dilation and effacement of the cervix. 2. Delivery of the baby. 3. Birth of the placenta.

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Dilation and effacement of the cervix.

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1. Dilation and effacement of the cervix. This is the longest stage of labor, lasting an average of 12 to 14 hours with a first birth and 4 to 6 hours with later births. Contractions of the uterus gradually become more frequent and powerful, causing the cervix, or uterine opening, to widen and thin to nothing, forming a clear channel from the uterus into the birth canal, or vagina

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delivery of the baby

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This second stage is much shorter than the first, lasting about 50 minutes for a first baby and 20 minutes in later births. Strong contractions of the uterus continue, but the mother also feels a natural urge to squeeze and push with her abdominal muscles. As she does so with each contraction, she forces the baby down and out.

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birth of the placenta

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Labor comes to an end with a few final contractions and pushes. These cause the placenta to separate from the wall of the uterus and be delivered in about 5 to 10 minute

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Unlike during pregnancy, during child birth high levels of infant cortisol and other stress hormones are

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adaptive. They help the baby withstand oxygen deprivation by sending a rich supply of blood to the brain and heart -In addition, stress hormones prepare the baby to breathe by causing the lungs to absorb any remaining fluid and by expanding the bronchial tubes (passages leading to the lungs). Finally, stress hormones arouse infants into alertness so they are born wide awake, ready to interact with their world

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This combination of a large head (with its well-developed brain) and a small body means that human infants

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learn quickly in the first few months of life. But unlike most other mammals, they cannot get around on their own until much later.

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To assess the baby's physical condition, doctors and nurses use the

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Apgar Scale. -a rating of 0, 1, or 2 on each of five characteristics is made at 1 minute and again at 5 minutes after birth. A combined Apgar score of 7 or better indicates that the infant is in good physical condition. If the score is between 4 and 6, the baby requires assistance in establishing breathing and other vital signs. If the score is 3 or below, the infant is in serious danger and requires emergency medical attention. Two Apgar ratings are given because some babies have trouble adjusting at first but do quite well after a few minute

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Apgar stands for

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-Appearance, heart rate -Pulse, reflex irritability -Grimace, muscle tone -Activity, and respiratory effort -Respiration.

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Freestanding birth centers

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permit greater maternal control over labor and delivery, including choice of delivery positions, presence of family members and friends, and early contact between parents and baby, also exist

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Natural, or prepared, childbirth consists of

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a group of techniques aimed at reducing pain and medical intervention and making childbirth as rewarding an experience as possible

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In a typical natural childbirth program, the expectant mother and a companion (a partner, relative, or friend) participate in three activities:

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-Classes. ? Relaxation and breathing techniques. ? Labor coach.

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classes

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The expectant mother and her companion attend a series of classes in which they learn about the anatomy and physiology of labor and delivery. Knowledge about the birth process reduces a mother's fear. encouragement and affection.

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relaxation and breathing techniques

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Expectant mothers are taught relaxation and breathing exercises aimed at counteracting the pain of uterine contractions.

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labor coach

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The companion learns how to help during child- birth by reminding the mother to relax and breathe, massaging her back, supporting her body, and offering encouragement and affection.

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Social support is important to the success of natural childbirth techniques.

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-These mothers had fewer birth complications, and their labors were several hours shorter than those of women who did not have supportive companionship. -and delivery—either by a lay birth attendant or by a relative or friend with doula training—less often have instrument-assisted or cesarean (surgical) deliveries or need medication to control pain. Also, their babies' Apgar scores are higher, and they are more likely to be breastfeeding at a two-month follow-up

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When natural childbirth is combined with delivery in a birth center or at home, mothers often

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give birth in an upright, sitting position rather than lying flat on their backs with their feet in stirrups (the traditional hospital delivery room practice). Use of special seats to enable an upright birth has become more common. When mothers are upright, labor is shortened because contractions are stronger and pushing is more effective. The baby benefits from a richer supply of oxygen because blood flow to the placenta is increased

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another increasingly popular method

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water birth, the mother sits in a warm tub of water, which supports her weight, relaxes her, and provides her with the freedom to move into any position she finds most comfortable. Water birth is associated with reduced maternal stress, shorter labor, and greater likelihood of medication-free delivery than both back-lying and seated positions. As long as water birth is carefully managed by health professionals, it poses no additional risk of infection or safety to mothers or babies.

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Analgesics

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drugs used to relieve pain, may be given in mild doses during labor to help a mother relax.

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Anesthetics

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a stronger type of painkiller that blocks sensation.

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Currently, the most common approach to controlling pain during labor is

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epidural analgesia, in which a regional pain-relieving drug is delivered continuously through a catheter into a small space in the lower spine. Unlike older spinal block procedures, which numb the entire lower half of the body, epidural analgesia limits pain reduction to the pelvic region. Because the mother retains the capacity to feel the pressure of contractions and to move her trunk and legs, she is able to push during the second stage of labor.

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Although pain-relieving drugs help women cope with childbirth and enable doctors to perform essential medical interventions, they also cause problems. Epidural analgesia, for example,

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weakens uterine contractions. As a result, labor is prolonged, and the chances of cesarean (surgical) delivery increase. And because drugs rapidly cross the placenta, exposed newborns tend to have lower Apgar scores, to be sleepy and withdrawn, to suck poorly during feedings, and to be irritable when awake. Although no confirmed long-term consequences for development exist, the negative impact of these drugs on the newborn's adjustment supports the current trend to limit their use.

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A small number of infants experience anoxia

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inadequate oxygen supply, during the birth process. Sometimes the problem results from a failure to start breathing within a few minutes. Healthy newborns can survive periods of little or no oxygen longer than adults can; they reduce their metabolic rate, thereby conserving the limited oxygen available. Nevertheless, brain damage is likely if regular breathing is delayed more than 10 minutes

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At other times, anoxia occurs during labor. A common cause is

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squeezing of the umbilical cord, a condition that is especially likely when infants are in breech position—turned in such a way that the buttocks or feet would be delivered first. Because of this danger, breech babies often experience a cesarean (surgical)

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An additional cause of oxygen deprivation is placenta abruptio

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premature separation of the placenta (complicating about 1 percent of pregnancies), a life-threatening event that requires immediate delivery. Factors related to it include multiple fetuses, advanced maternal age (40 and older), and teratogens that cause abnormal development of the pla- centa, such as tobacco and cocaine

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Still another condition that can lead to anoxia is Rh factor incompatibility between the mother's and baby's blood types.

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When the mother is Rh negative (lacks the Rh protein) and the father is Rh positive (has the Rh protein), the baby may inherit the father's Rh-positive blood type. If even a little of a fetus's Rh-positive blood crosses the placenta into the Rh-negative mother's bloodstream, she begins to form antibodies to the foreign protein. If these enter the fetus's system, they destroy red blood cells, reducing the supply of oxygen.

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effects of Rh factor incompatibility

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Mental retardation, miscarriage, heart damage, and infant death can occur. It takes time for the mother to produce antibodies, so firstborn children are rarely affected. The danger increases with each pregnancy. Fortunately, Rh incompatibility can be prevented in most cases. After the birth of each Rh-positive baby, Rh-negative mothers are given a vaccine to prevent the buildup of antibodies.

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After initial brain injury from anoxia

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another phase of cell death can occur several hours later. Placing anoxic newborns in a head-cooling device shortly after birth for 72 hours substantially reduces this secondary brain damage (detected through MRI brain scans) and increases scores on a newborn behavioral assessment -Another alternative—whole-body cool- ing by having anoxic newborns lie on a precooled water blanket—leads to an impressive reduction in death and disability rates during the first two years

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How do children who experience anoxia during labor and delivery fare as they get older?

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Research suggests that the greater the oxygen deprivation, the poorer children's cognitive and language skills in early and middle childhood. Although effects of even mild to moderate anoxia often persist, many children improve over time.

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For example, babies born more than six weeks early commonly have respiratory distress syndrome

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(otherwise known as hyaline membrane disease). Their tiny lungs are so poorly developed that the air sacs collapse, causing serious breathing difficulties. Today, mechanical respirators keep many such infants alive. In spite of these measures, some babies suffer permanent brain damage from lack of oxygen, and in other cases their delicate lungs are harmed by the treatment itself. .

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premature

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Babies born three weeks or more before the end of a full 38-week pregnancy or who weigh less than 51?2 pounds -highest among poverty-stricken women -Prematurity is also common in multiple births (twins or triplets)

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premature side effects

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Brain abnormalities, frequent illness, inattention, overactivity, sensory impairments, poor motor coordination, language delays, low intelligence test scores, deficits in school learning, and emo- tional and behavior problems are some of the difficulties that persist through childhood and adolescence and into adulthood

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Preterm infants

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those born several weeks or more before their due date. Although they are small, their weight may still be appropriate, based on time spent in the uterus.

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Small-for-date infants are

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below their expected weight considering length of the pregnancy. Some small-for-date infants are actually full-term. Others are preterm babies who are especially underweight.

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small-for-date infants usually have more serious problems.

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During the first year, they are more likely to die, catch infections, and show evidence of brain damage. By middle childhood, they are smaller in stature, have lower intelligence test scores, are less attentive, achieve more poorly in school, and are socially immature. Small-for-date infants probably experienced inadequate nutrition before birth. Perhaps their mothers did not eat properly, the placenta did not function normally, or the babies themselves had defects that prevented them from growing as they should. In some of these babies, an abnormally functioning placenta permitted ready transfer of stress hormones from mother to fetus. Consequently, small-for-date infants are especially likely to suffer from neurological impairments that permanently weaken their capacity to manage stress.

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The appearance and behavior of preterm babies

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can lead parents to be less sensitive and responsive in caring for them. Compared to full-term infants, preterm babies—especially those who are very ill at birth—are less often held close, touched, and talked to gently. At times, mothers of these infants resort to interfering pokes and verbal commands, in an effort to obtain a higher level of response from the baby. This may explain why preterm babies as a group are at risk for child abuse.

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A preterm baby is cared for

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in a special Plexiglas- enclosed bed called an isolette. Temperature is carefully controlled because these infants cannot yet regulate their own body temperature effectively. To help protect the baby from infection, air is filtered before it enters the isolette. When a preterm infant is fed through a stomach tube, breathes with the aid of a respirator, and receives medication through an intravenous needle, the isolette can be very isolating indeed! Physical needs that otherwise would lead to close contact and other human stimulation are met mechanically.

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These findings confirm that babies who are both preterm and economically disadvantaged

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intensive intervention. And special strategies, such as extra adult-child interaction, may be necessary to achieve lasting changes in children with the lowest birth weights.

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The Kauai study tells us

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that as long as birth injuries are not overwhelming, a supportive home environment can restore children's growth. But the most intriguing cases in this study were the handful of exceptions. A few children with fairly serious birth complications and troubled family environments grew into competent adults who fared as well as controls in career attainment and psychological adjustment. **Werner found that these children relied on factors outside the family and within themselves to overcome stress. Some had attractive personalities that drew positive responses from relatives, neighbors, and peers. In other instances, a grandparent, aunt, uncle, or babysitter provided the needed emotional support.

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infant mortality

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—the number of deaths in the first year of life per 1,000 live births—is an index used around the world to assess the overall health of a nation's children. -members of America's poor ethnic minorities are at greatest risk.

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Neonatal mortality

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the rate of death within the first month of life

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Two factors are largely responsible for neonatal mortality

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The first is serious physical defects, most of which cannot be prevented. The percentage of babies born with physical defects is about the same in all ethnic and income groups. The second leading cause of neonatal mortality is low birth weight, which is largely preventable.

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Besides financial hardship, some mothers have other reasons for not seeking early prenatal care.

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These include both situational barriers (difficulty finding a doctor, getting an appointment, and arranging transportation, and insensitive or unsatisfying experiences with clinic staff) and personal barriers (psychological stress, the demands of caring for other young children, family crises, lack of knowledge about signs of pregnancy and benefits of prenatal care, and ambivalence about the pregnancy). Many also engage in high-risk behaviors, such as smoking and drug abuse, which they do not want to reveal to health professionals

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Behavioral genetics

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a field devoted to uncovering the contributions of nature and nurture to this diversity in human traits and abilities.

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Heritability estimates

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measure the extent to which individual differences in complex traits in a specific population are due to genetic factors.

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Heritability estimates are obtained from

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kinship studies, which compare the characteristics of family members.

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Because the environments of most twin pairs are less diverse than those of the general population

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heritability estimates are likely to exaggerate the role of heredity.

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Perhaps the most serious criticism of heritability estimates has to do with their

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limited usefulness. They give us no precise information on how intelligence and personality develop or how children might respond to environments designed to help them develop as far as possible

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In sum, although heritability estimates

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confirm that heredity contributes to a broad array of complex traits, they tell us nothing about how environment can modify genetic influences. Still, scientists often rely on positive heritabilities before initiating more costly molecular analyses in search of specific genes that contribute to personality traits and disorders.

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gene-environment interaction

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which means that because of their genetic makeup, individuals differ in their responsive- ness to qualities of the environment

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Gene-environment interaction highlights two important points.

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First, it shows that because each of us has a unique genetic makeup, we respond differently to the same environment. Second, sometimes different gene- environment combinations can make two children look the same!

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canalization

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the tendency of heredity to restrict the development of some characteristics to just one or a few outcomes. A behavior that is strongly canalized develops similarly in a wide range of environments; only strong environmental forces can change it

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gene-environment correlation

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our genes influence the environments to which we are exposed.

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passive correlation

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because the child has no control over it. Early on, parents provide environments influenced by their own heredity.

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The second type of gene-environment correlation is evocative

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The responses children evoke from others are influenced by the child's heredity, and these responses strengthen the child's original style.

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in older children, active gene-environment correlation becomes common.

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As children extend their experiences beyond the immediate family and are given the freedom to make more choices, they actively seek environments that fit with their genetic tendencies. The well-coordinated, muscular child spends more time at after-school sports, the musically talented youngster joins the school orchestra and practices his violin, and the intellectually curious child is a familiar patron at her local library.

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niche-picking

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This tendency to actively choose environments that complement our heredity

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Accumulating evidence reveals that the relationship between heredity and environment

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is not a one-way street, from genes to environment to behavior. Rather, like other system influences considered in this and the previous chapter, it is bidirectional: Genes affect children's behavior and experiences, but their experiences and behavior also affect gene expression

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Stimulation

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—both internal to the child (activity within the cytoplasm of the cell, release of hormones into the bloodstream) and external to the child (home, neighborhood, school, and society)—modifies gene activity.

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Researchers call this view of the relationship between heredity and environment

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the epigenetic framework

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Epigenesis means

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development resulting from ongoing, bidirectional exchanges between heredity and all levels of the environment.

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