Question

a test cross is performed to determine an unknown genotype of an organism. which genotype must be used as the known genotype in order for the test cross to be successful?

heterozygous dominant
homozygous recessive
homozygous dominant

Explanation:

A test cross is a cross between an organism with an unknown genotype (usually dominant phenotype) and an organism with a homozygous recessive genotype. This is because the homozygous recessive organism can only contribute recessive alleles. By observing the phenotypes of the offspring, we can determine the unknown genotype. If the unknown is homozygous dominant (e.g., \(AA\)), all offspring will show the dominant trait when crossed with \(aa\) (\(Aa\) offspring). If the unknown is heterozygous (\(Aa\)), half of the offspring will show the recessive trait (\(Aa\) and \(aa\) in a 1:1 ratio).

Answer:

Homozygous recessive