In mice, frizzy hair is due to a mutant allele (fr) that is recessive to the wil

Question

In mice, frizzy hair is due to a mutant allele (fr) that is recessive to the wild type allele (Fr). The shaker phenotype in mice is due to a mutant allele (sh) that is recessive to the wild type allele (Sh). The two genes controlling these traits are on the same chromosome. When mice that were heterozygous for both genes was crossed to frizzy-haired, shaker mice the following progeny were obtained: straight-haired, shaker mice 40 straight-haired, non-shaking mice 10 frizzy-haired, shaker mice 5 frizzy-haired, non-shaking mice 45 a. If the Fr gene and the Sh gene were unlinked, how many mice would be expected in each phenotypic category? b. What is the map distance between the two genes? c. Draw a diagram of the chromosomes showing the arrangement of alleles of these two genes in the heterozygous parent.

Explanation / Answer

Answer:

3). a.

FrfrShsh (heterozygous mice) X frfrshsh (frizzy-haired, shaker mice)-----------Parents

frsh

FrSh

Frfr Shsh (straight-haired, non-shaking mice) 25

Frsh

Frfr shsh (straight-haired, shaker mice)25

frSh

frfr Shsh (frizzy-haired, non-shaking mice) 25

frsh

frfr shsh (frizzy -haired, shaker mice) 25

b).

Map distance between the genes = (%) Recombination frequency

Recombinantion frequency (RF) = (Total no of recombinants/Total progeny)* 100

RF = (15/100) *100

RF = 15%

Map distance = 15 map units

c).

Fr----------15 mu------------sh

fr----------15 mu------------Sh

frsh

FrSh

Frfr Shsh (straight-haired, non-shaking mice) 25

Frsh

Frfr shsh (straight-haired, shaker mice)25

frSh

frfr Shsh (frizzy-haired, non-shaking mice) 25

frsh

frfr shsh (frizzy -haired, shaker mice) 25

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