Chapter 15: The Chromosomal Basis of Inheritance – Flashcards
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What is the chromosome theory of inheritance?
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Mendelian genes have specific loci along chromosomes. Chromosomes undergo segregation and independent assortment.
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Explain the law of segregation.
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The law of segregation states that chromosomes are equally separated between haploid gametes.
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Explain the law of independent assortment.
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The inheritance of one trait has nothing to do, is independent from, the inheritance of another trait. Alleles/chromosomes are inherited and segregated independently from each other.
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What did Thomas Hunt Morgan use for his genetic studies? Why were these excellent test subjects?
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He used fruit flies, aka drosophila melanogaster. These were good test subjects because they reproduce very quickly, they are relatively inexpensive to grow/obtain/feed, and they have only 4 chromosomes which makes them easy to study and observe.
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Express the notation for a female fruit fly homozygous for red eyes, heterozygous for red eyes, and homozygous for white eyes.
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Xw+ Xw+, Xw+ Xw, Xw Xw
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What unusual result suggested that the eye color trait is located on the X chromosome for fruit flies?
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There was a higher prevalence of males with white eyes than females with white eyes. More females had the wild type eye color, red, not the mutant type.
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What are the many variations sex is determined for different species?
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X-Y system, mammals Z-W system, birds, fish, insects X-O system, grasshoppers, cockroaches, other insects Haplo-diploid system bees, ants
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What is the SRY gene? Where is it found and what does it do?
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"Sex determining Region of Y". it is a gene on the Y chromosomes that codes for testes formation.
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What is the definition of a sex-linked gene?
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A gene located on either sex chromosome
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In humans, how has the term sex linked gene been historically modified?
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The term generally means that the disease is carried on the X chromosome.
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Name three sex linked disorders
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Duchenne's muscular distrophy, hemophilia, and colorblindness
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What is Duchenne's muscular dystrophy?
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progressive weakening of muscles and loss of coordination. rarely live past their early 20s. caused by the absence of a muscle protein called dystrophin. this disease is sex linked
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What is hemophilia?
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an x linked recessive disorder caused by the absence of the proteins required for blood clotting. shows high prevalence in royal families
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What is a barr body? Why do females show a barr body in their cells?
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A barr body is a compact object, an inactive X chromosome that has condensed. Females only use what is coded for from one x chromosome, the other x chromosome becomes a barr body.
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What does x inactivation do?
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it maintains the proper gene dosage.
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How is the X chromosome in females inactivated?
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Methyl groups (-CH3) are attactch to the nitrogenous bases of the DNA. A particular region of the X chromosome is involved. The two regions from each X chromosome associate briefly during embryonic development, and then one becomes inactive and the other becomes a barr body.
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Why can you say that all calico cats are females?
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Color for cats is on the x chromosome. Calico/tortioseshell coloring is the result of a one black allele and one orange allele that come together in codominance. Males could never inherit this coloring since they only have one X chromosome, so can only be black or yellow.
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What are linked genes? Do linked genes sort independently?
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Linked genes are genes that are close together on the same chromosome and tend to be inherited together unless recombination occurs. They do not sort independently since they are found close to each other on the same chromosome. The closer a gene is to another on the chromosome, the less likely it is to recombine and be inherited with a different gene.
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If two genes are linked on the same chromosome, what is this combination called?
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the parental combination
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What are the offspring called that display new combinations from crossing over?
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recombinants or recombinant types.
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Review meiosis. When does crossing over occur?
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during prophase I
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Who is Alfred H. Sturtevant?
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A student of Thomas Hunt Morgan. Used assumptions from observations of crossovers to map genes. Created a linkage map
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What is a linkage map?
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A creation of Alfred H. Sturtevant. A linkage map uses recombination frequencies to estimate locations of genes on a chromosome in relation to one another. The lower the recombination frequency, the closer the two genes are to each other on the chromosome. Units of distance on a chromosome are measured in map units, a rather arbitrary unit that arises from the recombination frequencies (percentage).
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What is a map unit?
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1 map unit= 1% recombination frequency. Used in linkage maps of a chromosome
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What occurs in nondisjunction?
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Homolgous chromosomes or sister chromatids fail to separate in cell division. The result is gametes with incorrect chromosome counts.
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Explain aneuploidy
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An incorrect number of chromosomes in a fertilized zygote. Result of nondisjunction
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What is monosomy?
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When a cell is missing a chromosome (normal chromosome count is 2 of each). has 1 chromosome
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What is trisomy?
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When a cell has an extra chromosome (normal chromosome count is 2 of each) . has 3 chromosomes
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What is polyploidy?
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Having three or four chromosomal sets. more common in plants than in animals
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What is Down Syndrome? Symptoms? Inheritance?
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A disease caused by a third 21st chromosome (trisomy 21). causes intellectual deficits and physical changes. symptoms include flattened facial features, poor muscle tone, a small head, small height, short neck, and upward slanting eyes
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What is Kleinfelter? Symptoms? Inheritance?
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A boy is born with an extra X chromosome. this disease may go undetected until adulthood based on severity. symptoms include small testicles, taller than average, absent/delayed/incomplete puberty, enlarged breast tissue, shyness, intellectual delays, and attention difficulties.
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What is Turner Syndrome? Symptoms? Inheritance?
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When a woman only has one X chromosome. signs and symptoms for this disease vary extremely. Some examples of symptoms include a receeding or small jaw, short fingers or toes, unable to conceive a child, learning and social disabilities.
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What is Cri du Chat? Symptoms? Inheritance?
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a disease that occurs when a portion of the 5th chromosome is missing. causes abnormal larynx development, small size at birth, cry like a cat, small head, wide set eyes
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What is Chronic Myelogenous Leukemia? Symptoms? Inheritance?
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mutation of chromosome 9 and 22, allows blood cells to grow out of control, causes too many white blood cells. symptoms include easy bleeding, fever, fatigue, night sweats
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What results from the genotype "XXY" ?
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A male with Kleinfelter syndrome. Symptoms include small testes, sterility, breast enlargement, female characteristics, and subnormal intelligence.
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What results from the genotype "XXX" ?
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A female with trisomy x. Symptoms include being slightly taller than average and being at risk for learning disabilities.
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What results from the genotype "XO" ?
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A female with turner syndrome. Symptoms include being sterile and having sex organs that do not mature (not going through puberty)
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What results from the genotype "XYY" ?
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A male that does not undergo normal sexual development and is taller than average.
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What happens in a deletion?
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A chromosomal fragment is lost
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What happens in a duplication?
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Extra gene is added
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What happens in an inversion?
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Order of genes is reversed
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What happens in a translocation?
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A portion of the lost fragment joins a non-homologous chromosome.
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What is genomic imprinting?
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a zygote expresses only one allele of an imprinted gene depending on which parent passed the allele along. ex. igf2 gene in mouse that codes for insulin.
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What group of genes have you inherited only from your mother?
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Mitochondrial DNA, "extranuclear genes", or "cytoplasmic genes"
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What are some diseases carried through mitochondrial DNA?
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defects in atp synthase proteins, mitochondrial myopathy which causes weakness, an intolerance to exercise, and muscle deterioration. also levers hereditary opt neuropathy, causes sudden blindness in people in young 20s or 30s. mitochondrial dna might also contribute to diabetes, heart disease, and alzheimers
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Why are extranuclear genes inherited maternally?
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The zygote's cytoplasm comes from the egg (female)
