Q.The test cross involves :

A test cross is defined as crossing the F1 hybrid with the homozygous ('double') recessive genotype, to reveal the hybrid's own genotype from the resulting offspring ratio.

Working

A test cross is a specific type of cross used in genetics to determine whether an individual displaying a dominant phenotype is homozygous dominant or heterozygous, and more generally to reveal the types and proportions of gametes an individual produces. It is carried out by crossing the individual of interest -- typically the F1 hybrid, which shows the dominant phenotype but whose exact genotype is not directly visible -- with an individual that is homozygous recessive for the trait(s) concerned, i.e. carries two recessive alleles ('double recessive', for example aa for a single trait, or aabb for two traits). Since the homozygous recessive parent can only contribute recessive alleles to every offspring, the phenotype of each offspring directly reflects the particular allele combination contributed by the hybrid parent's gamete. This is precisely what option (a) …