Genetics 14. A testcross is always performed between the individual that is heterozygous for the genes to be mapped and an individual who is ____________. A. heterozygous for the genes B. homozygous dominant for the genes C. homozygous recessive for the genes D. lacking the genes E. None of these choices are correct C. homozygous recessive for the genes 15. While mapping two genes in Drosophila, you observe 30 recombinants among 200 total offspring. What is the distance between these genes? A. 30 map units B. 6.67 map units C. 200 map units D. 15 map units D. 15 map units 16. A map distance of 23.6 between two genes indicates which of the following? A. The genes are 23.6 millimeters apart B. There are 23.6 other genes between the two genes of interest C. 23.6% of the offspring exhibit recombination between the two genes D. 23.6% of the offspring do not survive C. 23.6% of the offspring exhibit recombination between the two genes 17. The individual who is credited with producing the first genetic linkage map is _____. A. Thomas Hunt Morgan B. Gregor Mendel C. Alfred Sturtevant D. Barbara McClintock C. Alfred Sturtevant 18. In a mapping experiment with three genes, which phenotype should occur most often in the F2 offspring? A. Parental phenotypes B. Phenotypes of individuals with single crossover events C. Phenotypes of individuals with double crossover events D. All of these choices should be equal in the F2 generation A. parental phenotypes 19. The middle gene of a three gene mapping experiment can be determined by examining the genotypes of which of the following? A. Offspring that resemble the parents B. Offspring that exhibit a single crossover event C. Offspring that exhibit double crossover events D. None of these choices are correct C. offspring that exhibit double crossover events 20. In a given mapping experiment, you expect that incidence of double crossovers is 3.5%, but you only observe 2.5%. This can be explained by ________________. A. interference B. linkage C. coincidence D. segregation A. interference 21. You have calculated the interference value for a given mapping experiment to be 30%. What does this mean? A. 30% more double crossovers occurred than expected B. 30% fewer double crossovers occurred than expected C. 70% more double crossovers occurred than expected D. 70% fewer double crossovers occurred than expected B. 30% fewer double crossovers occurred than expected