In chickens, a single mutation has a dominant effect on neck feathers (causing the chickens to have "naked necks") and a recessive effect on viability (causing the chickens to die early). Let N be the mutant allele and n the wild-type allele.

A) Male chickens with naked necks are crossed to females with normal neck feathers. Think about the genotypes of those chickens. Among the F1 progeny, what % naked neck versus normal neck feather adult chickens do you expect?
B) Male chickens with naked necks are crossed to females with naked necks. Among the F1 progeny, what % naked neck versus normal neck feather adult chickens do you expect?

As a single mutation has inferred, hence we can assume that the genotype of the male chickens with naked necks will be Nn. The female chickens with normal neck feathers will have the genotype nn. To depict the outcomes of a cross between them, lets generate a punnet square:

n n

N Nn Nn

n nn nn

The results from the punnet square show that 50% of the offsprings will have the probability to have naked neck and 50% of the offsprings will have normal neck.