Download 1. True or false? Genes that are located sufficiently close together in

1. True or false? Genes that are located sufficiently close together in a chromosome do not undergo linkage, they are said to be assorted independently. False 2. True or false? Crossing‐over between homologous chromosomes results in recombination that breaks up combinations of linked alleles. True 3. True or false? The map distance between genes in a genetic map is not related to the rate of recombination between the genes. False 4. True or false? A genetic map depicts the relative positions of introns along a chromosome. False 5. True or false? Recombination cannot take place between nucleotides within a single gene. False 6. The maximum recombination frequency between two genes is A. 100%. B. 80%. C. 50%. 9 D. 10%. E. 1%. 7. In the absence of recombination, what ratio of phenotypes is expected in the progeny of the cross aB/Ab X AB/ab? A. 3 A‐B‐ : 1 aabb B. 1 aaB‐ : 2 A‐B‐ : 1A‐bb 9 C. 9 A‐B‐ : 3 A‐bb : 3 aaB‐ : 1 aabb D. the ratio depends on the distance between genes. E. the ratio depends on the interference. 8. Recombination frequencies A. are the same for all genes. B. arise from completely random genetic exchange. C. are the same for cis and trans heterozygotes. 9 D. decrease with distance. 9. What does the coefficient of coincidence measure? A. the frequency of double crossovers. B. the ratio of double crossovers to single crossovers. C. the ratio of single crossovers in two adjacent regions. D. the ratio of double crossovers to the number expected if there were no interference. 9 E. the ratio of recombinant to parental progeny. 11. Three‐point testcrosses A. detect double crossing over events. Page 1 B. require heterozygous gametes. C. determine gene order on a chromosome. D. both A and B. E. both B and C. F. both A and C. 9 12. A coefficient of coincidence of 0.25 means that A. the frequency of double crossovers is 1/4. B. the frequency of double crossovers is 1/4 of the number expected if there were no interference. 9 C. there were four times as many single crossovers as double crossovers. D. there were four times as many single crossovers in one region as there were in an adjacent region. E. there were four times as many parental as recombinant progeny. 13. The ratio of the observed double crossovers divided by the expected number of double crossovers is the A. interference level. B. resistance level. C. coefficient of coincidence. 9 D. coefficient of selection. E. coefficient of coupling. F. frequency of recombination. 14. A trans‐heterozygote has a A. mutant phenotype if mutations are in different genes. B. mutant phenotype if mutations are allelic. C. wildtype phenotype if mutations are in different genes. D. wildtype phenotype if mutations are in the same gene. E. A and D F. B and C 9 15. Genes ho and dp are 9.0 map units apart, and genes dp and da are 26.3 map units apart (gene order is ho ‐ dp – da). In the absence of interference, what is the probability of a double crossover in these regions? A. 0% B. 2.4% 9 C. 9.0% D. 17.3% E. 35.3% 16. The Drosophila genes for white eyes (w), cut wings (ct) and tan body (t) lie at map positions 1.5, 20.0 and 27.5, respectively. Out of 576 progeny, 6 are double crossovers. What is the degree of interference? A. 1.4% B. 6.0% C. 7.5% Page 2 D. 18.5% E. 25.0% 9 17. Genes which do not undergo independent assortment but are transmitted together are said to be linked. 18. The physical exchange of segments between homologous chromosomes is called crossing‐over. 19. A diagram of a chromosome showing the relative positions of the genes constitutes a genetic map. 20. One map unit of a genetic map may be called a centimorgan. 21. Physically, 1 map unit corresponds to a length of the chromosome in which, on the average, one crossover is formed in every 50 cells undergoing meiosis. 22. Crossing‐over takes place at the four ‐ strand stage of meiosis. 23. The cross‐shaped exchange configuration between nonsister chromatids of homologous chromosomes is called a chiasma. 24. Chiasmata are observed in prophase I of meiosis. 25. The tendency for crossing‐over to inhibit the formation of another crossover nearby is called interference. 26. When there is a nonrandom choice of chromatids in successive crossovers, the phenomenon is called chromatid interference.
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