An individual with a dominant phenotype is crossed with an individual with a recessive phenotype. Five out of nine offspring show the dominant phenotype. What is the genotype of the dominant parent?
A) homozygous dominant
B) heterozygous
C) homozygous recessive
D) either homozyous dominant or heterozygous
E) There is not enough information to determine the genotype of the dominant parent.

Question

Quizplus · Accepted Answer

If five out of nine offspring have the dominant phenotype, then the ratio of dominant to recessive offspring is 5:4. This is close to a 1:1 ratio, which suggests that the dominant parent is likely heterozygous (i.e. has one dominant allele and one recessive allele). If the dominant parent was homozygous dominant, then we would expect a 100% dominant phenotype in the offspring. If the dominant parent was homozygous recessive, then all of the offspring would be heterozygous and show the dominant phenotype, which is not the case. Therefore, the best choice is B, heterozygous.

An Individual with a Dominant Phenotype Is Crossed with an Individual