Question

The best method to determine the presence of a recessive allele for white hair on a black haired guinea pig (whose both parents are black) would be

• A. Mate the guinea pig with another black guinea pig and look for white offspring
• B. Look for white hairs on the guinea pig.
• C. Mate the guinea pig with a white guinea pig and look for white offspring.
• D. Observe the chromosomes of a hair cell from a black hair.
• E. See if the guinea pig has any white siblings.

Answer 1

The correct option is C Mate the guinea pig with a white guinea pig and look for white offspring.

A test cross is performed to determine the genotype of a dominant parent if it is a heterozygous or homozygous dominant. For the purpose, a dominant parent is crossed with the homozygous recessive parent. A test cross between a heterozygous dominant (carrying one copy of dominant and recessive allele each) and recessive parent obtains dominant and recessive offspring in 1:1 ratio. A test cross between a homozygous dominant (carrying two copies of the dominant allele) and recessive parent obtains all dominant offspring. If a cross between the black haired guinea and white guinea obtains all black offspring; the tested "black haired guinea" is homozygous. If a cross between the black haired guinea and white guinea obtains black and white offspring in 1:1 ratio; the tested "black haired guinea" is heterozygous.

Therefore, the correct answer is option C.