A testcross is
A)A mating between an individual of unknown genotype and an individual homozygou recessive for the trait of interest
B)a mating between an individual of unknown genotype and an individual heterozygous for the trait of interest
C)a mating between two individuals of unknown genotype
D)a mating between an individual of unknow genotype and an individual homozygous dominant for the trait of interset
E)a mating between two individuals heterozygous for the trait of interest.