Question

Red hair in humans is recessive, whereas dark hair is dominant, Suppose that a red-haired male and a heterozygous female have a male child who then mates with a heterozygous female.

a) What is the probability that the grandchild is pure dark-haired?

b) What is the probability that the grandchild is dark-haired?

c) What is the probability that the grandchild is red-haired?

Answer 1

a)probability that the grandchild is pure dark-haired =P(male child is heterozygous and both parent gives dark trait to grandchild

=(1/2)*(1/2)*(1/2)=1/8

b)

probability that the grandchild is dark-haired =P(male child is heterozygous and at least parent gives dark trait to grandchild)+P(male child is red haired and female parent gives dark trait to grandchild)

=(1/2)*(1-non of them gives dark trait to grandchild)+(1/2)*(1/2)=(1/2)*(1-(1/2)*(1/2))+(1/2)*(1/2) =5/8

c)

probability that the grandchild is red-haired =1-P(dark haired)=1-5/8 =3/8