Question

Albinism in humans is inherited as a simple recessive trait.  For the following families, determine the genotypes of the parents.  When two alternative genotypes are possible, list both.

1. Two non-albino (normal) parents have five children, four normal and one albino.  
2. A normal male an albino female have ten children, all normal.

Answer 1

a) both parents are normal but they have a child with albinism, so both parents are carriers of albinism.

let the alleles be A- normal, a- albinism.

Aa * Aa

	A	a
A	AA ( normal)	Aa ( normal)
a	Aa ( normal)	aa ( albinism)

they can have both normal children and children with albinism.

so the genotype of the parents are Aa.

b) normal male and albino female, have 10 children all are normal

since the female has albinism her genotype is aa, the male is normal and all 10 of their children are normal so he has the dominant allele A, he can be either AA or Aa.

Aa * aa

	A	a
a	Aa ( normal)	aa ( albinism)

it is possible to have both normal and albino children

AA * aa

Aa ( all F1 progenies are normal)