Question

In mice ears may have tufts of hair or be normal (no tufts), and the ears may be long or short. A normal, short-eared parent was crossed with a tufted, long-eared parent. All the F1 had normal, short ears. The F1 was crossed with itself with the following results (F2): 78 Normal, short ears 26 Tufted, long ears a. Give the predicted phenotypic frequencies for the F2 generation if the two genes are unlinked. b. Give the predicted phenotypic frequencies for the F2 generation if the two genes are tightly linked. c. Do the observed frequencies support the hypothesis that these are linked or unlinked genes?

Answer 1

a). If the genes are unlinked, 4 types of phenotypes would be arised according to Mendel experiments as follows..

Normal, short-eared (NNEE) x tufted, long-eared (nnee)----Parents

NnEe (normal, short-eared)----------------------------------------F1

F1 x F1

F2 Phenotypes:

Normal, short-eared (T_E_) = 9/16

Normal, long-eared (T_ee) = 3/16

Tufted, short-eared (ttE_) = 3/16

Tufted, long-eared (ttee) = 1/16

b). If the genes are completely linked, the following results will be come.

NE/NE x ne/ne----Parents

NE/ne-------------F1

NE ne

NE NE/NE (normal, short-eared) NE/ne (normal, short-eared)

ne NE/ne (normal, short-eared) ne/ne (tufted, short-eared)

Normal, short-eared (T_E_) = 3/4

Tufted, long-eared (ttee) = 1/4

c). The observed frequencies support the hypothesis that these are linked genes.