What is test cross? Mention its significance.

The crossing of an F${}_1$ progeny with a double (homozygous) recessive parental progeny is done in order to determine whether the progeny is homozygous or heterozygous for a character under consideration. This is called as test cross.

Significance:

The test cross is performed to determine the genotype of a dominant parent if it is a heterozygous or homozygous dominant. On the basis of the results obtained in the ratio of the offspring, it can be predicted that the parent is having which genotype. If all the offsprings are of same phenotype, then the parent is homozygous dominant. If there is 1:1 ratio in the phenotype of the organisms, the parent is heterozygous dominant.