1. A. The A locus and D locus are so tightly linked that no recombination is eve
ID: 52874 • Letter: 1
Question
1. A. The A locus and D locus are so tightly linked that no recombination is ever observed between them. If Ad/Ad is crossed to aD/aD and the F1 is intercrossed, what phenotypes will be seen in the F2 and in what proportions. Remember: Ad/Ad is another notation for
A d
A d and so on for aD/aD.
A female animal with genotype AaBb is crossed with a male aabb. Their progeny include 442 AaBb, 458 aabb, 46 Aabb and 54 aaBb. Explain these results.
A fruit fly of genotype BR/br is testcrossed to br/br. In 84 percent of the meioses, there are no crossovers between the two genes; in 16 percent of the meioses, there is one crossover between the two genes. What proportion of the progeny will be Br/br?
Explanation / Answer
F2 phenotype proportion = 1:2:1 ie;1- AdAd, 2- AdaD, 1-aDaD
Heterozygote trait of female AaBb crossed with homozygous trait of male aabb
Homozygous for both recessive traits = 458 progeny
Heterozygous for both dominant traits = 442 progeny
recessive for trait bb = 46 progeny
Recessive fro trait aa = 54 progeny
0.5
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