A maternal effect gene exists in a dominant N (normal)allele and a recessive n (

Question

A maternal effect gene exists in a dominant N (normal)allele and a recessive n (mutant) allele. How would the results differ in the reciprocal sets of crosses?
nn female x NN male --> F1 --> F2
NN female x nn male --> F1 --> F2

A.) In the first set of crosses, all the F1s would be mutant and all the F2s would be mutant, but in the second set of crosses all the F1s would be normal and all the F2 would be mutant.

B.) In the first set of crosses, all the F1s would be mutant and all the F2s would be normal, but in the second set of crosses all the F1s would be normal and all the F2 would be normal.

C.) In the first set of crosses, all the F1s would be mutant and all the F2s would be normal, but in the second set of crosses all the F1s would be mutant and all the F2 would be mutant.

D.) In the first set of crosses, all the F1s would be mutant, but in the second set of crosses all the F1s would be normal. In both sets of crosses the F2 generation would show a 3:1 ratio of normal:mutant.

Explanation / Answer

Option D is correct) In the first set of crosses, all the F1s would be mutant, but in the second set of crosses all the F1s would be normal. In both sets of crosses the F2 generation would show a 3:1 ratio of

Reason Cross 1.

nn female X NN male

F1 – Nn (All mutant because maternal allele n is mutant)

Nn X Nn

NN, Nn, Nn, nn (3:1 ratio as NN is normal and rest are mutant)

Cross 2: NN female X nn male

Nn F1   (all normal)

Nn X Nn   (Normal as n comes from male)

NN, Nn, Nn, nn (N from females ) 3:1 because of Nn will be mutant

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