Chapter 13 Ap Bio – Flashcards
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Life Cycle
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The generation to generation sequence of stages of the reproductive history of an organism; from conception to production of its own offspring.
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Somatic Cell
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Any cell other than a gamete- has 46 chromosomes
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Karyotype
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A display of condensed chromosomes arranged in pairs. Used to screen for abnormal numbers of chromosomes or defective chromosomes associated with certain congenital disorders, such as down syndrome.
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Homologous Chromosomes
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The 2 chromosomes composing a pair have the same length, centromere position, and staining pattern; also called homologues. Both chromosomes in a pair carry genes controlling the same inherited characteristics.
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Sex Chromosomes
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X and Y chromosomes - determine an individuals sex
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Autosomes
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The other chromosomes (not the X and Y sex chromosomes). 22 pairs (in humans).
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Diploid Cell
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Any cell with 2 chromosome sets; has a diploid number of chromosomes, abbreviated 2n. (ex. humans=2n=46)
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Haploid Cell
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Any cell with 1 chromosome set (gametes=egg and sperm); each has n chromosomes (haploid #). (ex. humans=n=23)
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Fertilization
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Union of gametes (sperm and ovum), culminating in fusion of their nuclei. Restores the diploid condition, forming a zygote. The diploid zygote develops into an adult (as a result of mitotic cell division).
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Zygote
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The egg resulting from fertilization; diploid, as it contains 2 haploid sets of chromosomes bearing genes representing the maternal and paternal family lines.
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Meiosis
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Cell reproductions; a 2 stage type of cell division in sexually reproducing organisms, resulting in cells with half the chromosome # of the original cell.
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How are karyotypes prepared?
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-Prepared from isolated somatic cells -Somatic Cells are treated with a drug to stimulate mitosis and then grown in culture for several days. -A slide of cells arrested in metaphase is stained and then viewed with a microscope equipped with a digital camera. -A digital photograph of the chromosomes is entered into a computer and the chromosomes are electronically rearranged into pairs according to size and shape.
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What are the three different types of life cycles?
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animals, plants and some algae, and most fungi and some protists (including algae)
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Describe the animal life cycle.
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Gametes (haploid cells), are produced during meiosis, and undergo no further cell division prior to fertilization. The diploid zygote divides by mitosis, producing a multicellular organism that is a diploid.
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Describe the plants and some algae life cycle.
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-alteration of generations -diploid and haploid multicellular stages -multicellular diploid stage: (sporophyte) haploid cells called spores are produced. These cells give rise to a multicellular individual without fusing with another cell. -Spore divides mitotically to generate a multicellular haploid stage called the gametophyte (haploid), which makes gametes by mitosis. -Fertilization among the haploid gametes results in a diploid zygote, developing into the next sporophyte generation.
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Describe the fungi and some protists, including algae life cycle.
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(only diploid stage=1 celled zygote) -gametes fuse and form a diploid zygote -meiosis occurs without a diploid offspring developing. -meiosis produces haploid cells that divide by mitosis, and give rise to a haploid multicellular adult organism. -The haploid organism carries out mitosis, whose product cells develop into gametes.
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What exactly is meant by "alternation of genes"?
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A life cycle in which there is both a multicellular diploid form (sporophyte), and a multicellular haploid form (gametophyte). It is a characteristic of plants and some algae. Fertilization and meiosis alternate in sexual life cycles.
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What are the two broad goals of meiosis?
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-Produces gametes -Introduces variability among the gametes
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Living organisms are distinguished by...
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there ability to produce their own kind.
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Heredity
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The transmission of traits from one generation to the next
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Variation
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Shows that offspring differ in appearance from parents and siblings. (usually refers to phenotype)
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Genetics
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The scientific study of heredity and variation
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Phenotype
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What we see
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Genotype
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What we don't see
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What is the role of a gene?
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They carry traits. inherited from parents to offspring.
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What are genes?
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The units of heredity Segments of DNA
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Each gene...
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has a specific locus on a certain chromosome
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One set of chromosomes...
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is inherited from each parent (maternal and paternal)
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Gametes
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(Reproductive cells) - sperm and eggs - unite, passing genes to the next generation (in sexual reproduction).
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Asexual Reproduction
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One parent produces genetically identical offspring by mitosis. (ie. budding)
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Sexual Reproduction
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Two parents give rise to offspring that have unique combinations of genes inherited from the two parents.
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What are the sex chromosomes?
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X and Y
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Human Females...
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XX
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Human Males...
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XY
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Synthesis (S-phase) of the Cell Cycle
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-each chromosome is replicated -each replicated chromosome consists of 2 identical sister chromatids.
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Each set of 23 chromosomes consists of...
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22 autosomes and a single sex chromosome
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ovum sex chromosome
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X
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sperm sex chromosome
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X or Y
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The sperms sex chromosome...
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determines the gender of the next generations child.
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At sexual maturity, ovaries and testes produce...
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Haploid gametes
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gametes in meiosis
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GAMETES ARE THE ONLY TYPES OF HUMAN CELLS PRODUCED BY MEIOSIS.
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cells that are not sex cells in the human body are produced by...
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mitosis
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Meiosis results in
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One set of chromosomes in each gamete. (half as many as the parent cell - or haploid cell - had). 4 daughter cells consisting of the above characteristics.
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The three sources of genetic variation in mitosis are...
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-Independent assortment of chromosomes -Crossing over -Random Fertilization
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Genetic variation in offspring results from...?
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Meiosis (true for all life cycles) Mutations
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Meiosis
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Preceded by the replication of chromosomes during the S-Phase of interphase (so, all the chromosomes are double stranded; that is, they each consist of identical sister chromatids attached at the centromere when meiosis starts).
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Two sets of cell divisions in meiosis
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Meiosis I Meiosis II
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Meiosis I
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Homologous chromosomes come together Homologous pairs separate Results in 2 haploid daughter cells with replicated chromosomes
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Meiosis II
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Sister chromatids separate Results in 4 haploid daughter cells with unreplicated chromosomes
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Meiosis I is also known as what?
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The Reduction Division
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How many phases does Meiosis I have?
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4
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Prophase I
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Longest phase; chromosomes begin to condense. Synapsis: Homologous chromosomes loosely pair up, aligned gene by gene. Crossing over: Nonsister chromatids exchange DNA segments. Tetrad: (Result of crossing over) - formed by a pair of chromosomes, a group of 4 chromatids. Chiasmata: (each tetrad usually has one or more) - X shaped regions where crossing over occured.
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Metaphase I
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Tetrads line up at the metaphase plate (Pairs of homologous chromosomes) - one chromosome facing each pole. Microtubules of spindle - from each pole they attach to the kinetochore of one chromosome.
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Anaphase I
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Pairs of homologous chromosomes separate. Sister chromatids are still attached to each other at the centomere of each chromosome. One chromosome moves towards each pole, guided by the spindle apparatus.
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Telophase I
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As telophase begins, each half of the cell has a haploid set of chromosomes; each chromosome still consists of 2 sister chromatids.
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Cytokinesis
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Happens along with telophase Two haploid daughter cells form Animal Cells - cleavage furrow forms Plant Cells - cell plate forms
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What DOESNT happen between meiosis I and meiosis II?
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Chromosome replication. (The chromosomes are already replicated; the sister chromatids will separate during meiosis II.
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Meiosis II is similar to what?
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Mitosis
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Prophase II
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A spindle apparatus forms In late prophase II - chromosomes move towards the metaphase plate.
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Metaphase II
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Sister chromatids arranged at the metaphase plate. -crossing over: sister chromatids are no longer genetically identical -Kinetichores of sister chromatids: attach to microtubules, extending from opposite poles.
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Anaphase II
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The sister chromatids separate Now move as 2 newly individual chromosomes toward opposite poles.
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Telophase II and Cytokinesis
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Chromosomes arrive at opposite poles -Nuclei forms, chromosomes begin decondensing. -Cytokinesis: separates the cytoplasm
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At the end of meiosis
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there are four haploid cells. each daughter cell is genetically distinct from the others and from the parent cell.
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Number of chromosomes in the daughter cells of mitosis
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conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell.
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Number of chromosomes in the daughter cells of meiosis
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reduces the # of chromosome sets from 2 (diploid) to one (haploid), producing cells the differ genetically from each other and form the parent cell.
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Three events that are unique to meiosis (all take place in meiosis I)
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Synapsis and Crossing Over Tetrads Homologous chromosomes separate instead of the sister chromatids
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Synapsis and Crossing Over
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Prophase I Homologous chromosomes physically connect and exchange genetic information.
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Tetrads
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At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual repliated chromosomes, (metaphase I).
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The homologous chromosomes separate
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(At anaphase I) - instead of the sister chromatids, and are carried to the opposite poles of the cell.
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DNA replication in Meiosis and Mitosis occurs during which phase?
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Interphase
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Divisons in mitosis vs meiosis
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mitosis - 1 meiosis - 2
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Synapsis and Crossing Over in mitosis vs meiosis
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mitosis - does not occur meiosis - Form tetrads in prophase I
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Daughter Cells, Genetic composition in mitosis vs meiosis
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mitosis - 2 diploid, identical to parent cell meiosis - 4 haploid, different from parent cell and each other
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Role in animal body in mitosis vs meiosis
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mitosis - produces cells for growth and tissue repair meiosis - produces gametes
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Genetic variation produced in sexual life cycles contributes to what?
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evolution
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Mutations
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-Changes in an organism's DNA -Original source of genetic diversity; create different versions of genes
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Sexual Reproduction (Genetic Variation)
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Reshuffling of different versions of genes; produces genetic variability
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Independent Assortment of Chromosomes
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-Homologous pairs of chromosomes orient randomly at metaphase I of meiosis -Each pair of chromosomes sorts maternal and paternal homolouges into daughter cells independently of the other pairs -The number of combinations possible when chromosomes assort independently into gametes is 2^n -For humans, there are more than 8 million possible combinations of chromosomes from independent assortment (2^23=____)
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Crossing Over
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-Produces recombinant chromosomes, which combine genes inherited from each parent. -Begins very early in Prophase I, as the homologous chromosomes pair up gene by gene -Homologous portions of two nonsister chromatids trade places
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Random Fertilization
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-Any sperm can fuse with any ovum (unfertilized egg) to form the diploid zygote -The resulting zygote will have any one of about 64 trillion diploid combinations -Crossing over adds even more variation -Each zygote has a unique genetic identity
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Evolutionary Signifigance of Natural Selection within Populations
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Results in accumulation of genetic variations favored by the environment.
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Evolutionary Signifigance of Sexual Reproduction within Populations
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Contributes to the genetic variation in a population, which ultimately results from mutations.
