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Unformatted text preview: Name ____________ KEY _____________________________________ page 1 B/Z 350 2nd Hour Exam Spring 2010 Answer all questions in the space provided on the exam. Questions 1-5 are worth 2 points each. Put answers in the underlined spaces at the left. X chromosome 1 A Barr body is a lyonized (heterochromatic) ____. 1/8 2. A person shares ____ (a fraction) of her/his genes with her/his first cousin. 50 3. If two loci are not linked, the map distance between them will be approximately ____ map units (cM). Fluorescence in situ hybridization 4. In cytogenetics, FISH is an acronym that stands for ____. quantitative 5. Another name for a polygenic trait is a ____ trait. Questions 6 - 12 are worth five points each. For full credit, answer in full sentences and show any math required. 6. Even though Drosophila melanogaster (fruit fly) males normally have one X and one Y chromosome, explain why sex determination in Drosophila is more like an XO sex determining system than an XY system. In Drosophila melanogaster the male sex is not determined by the presence of a Y chromosome, but by the ratio of one X chromosome to two sets of autosomes, just as in XO sex determining systems. 7. Based on this pedigree for a rare recessive autosomal trait, what is the probability that the mother of the child marked with a question mark is a heterozygote? The probability that the mother of the child is a heterozygote is ( x =) (= 0.25 or 25%) because her grandfather would have to be a heterozygote since his mother is a homozygote, and there is a chance that he passed the allele to her father and a chance her father passed the allele to her. ____________ KEY ________________________________name page 2 8. Define penetrance in regard to genotype. Penetrance is the fraction (frequency) of individuals with a genotype that express the expected phenotype. 9. If we say two loci are separated by 3.2 cM (m.u.), what does this mean? It means that 3.2% of the offspring from a test cross of a linked dihybrid are recombinant....
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