Precursor rightarrow Intermediate rightarrow product enzyme A enzyme B A= functi

Question

Precursor rightarrow Intermediate rightarrow product enzyme A enzyme B A= functional enzyme, a= nonfunctional enzyme B= functional enzyme, b= nonfunctional enzyme AAbb individuals are crossed to aaBB individuals. The FI cross with one another and the phenotypes of their progeny are scored as: 4 white mice: 9 yellow mice: 3 red mice. The results indicate that the coloring produced by the precursor, intermediate and product are A red, white, yellow respectively B white, red, yellow respectively C yellow, white, red respectively D yellow, red white respectively E none of the above

Explanation / Answer

The progeny a first cross is AaBb via Ab gametes produced by both parents. Further cross between F1-

There are four instances when both alleles of enzymeA are not functioning, it will correspond to precursor state ie white mice.

There are the instances when either one of alleles of enzymeA are functional but both of enzymeB are not, it will correspond to intermediate state ie red mice.

When either one of enzymeA and enzymeB allele is dominant, 9 combinations are possible corresponding to product ie yellow mice. So answer is B.

AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBa Aabb aaBb aabb

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