In fruit flies, an X-linked dominant mutant allele of the Notch gene (N)causes Notched wings in heterozygous females but is lethal in hemizygous or homozygous condition.What ratio of offspring would be observed in a cross of a Notched-wing female with a normal male?
A)1/3 Notched-wing females, 1/3 normal females, 1/3 normal males
B)1/4 Notched-wing females, 1/4 normal females, 1/4 Notched-wing males, 1/4 normal males
C)1/2 Notched-wing females, 1/2 normal males
D)1/2 normal females, 1/2 Notched-wing males
E)2/3 Notched-wing females, 1/3 normal males

Question

Quizplus · Accepted Answer

The Notch gene is X-linked and dominant. In heterozygous females, one copy of the normal allele and one copy of the mutant allele are present. This results in the Notched-wing phenotype. In hemizygous or homozygous condition, two copies of the mutant allele are present, which is lethal. In a cross of a Notched-wing female with a normal male, the female will contribute one X chromosome with the mutant allele and one X chromosome with the normal allele. The male will contribute one X chromosome with the normal allele. The offspring will be 1/3 Notched-wing females, 1/3 normal females, and 1/3 normal males.

In Fruit Flies, an X-Linked Dominant Mutant Allele of the Notch