Question

How does a test cross help in identifying the genotype of the organism? Explain.

Answer 1

A test cross is carried out to find out whether an organism having a dominant phenotype is homozygous or heterozygous for the trait. In a test cross, the cross is carried out between a homozygous recessive organism and another organism showing the dominant phenotype.
i) If the organism showing the dominant phenotype has homozygous alleles than the resulting F1 generation will have organisms all of which show the dominant character and their genotype will be heteozygous for the trait.
ii) However, if the organism has a heterozygous genotype for the dominant trait then the resulting F1 generation will have half of the organisms of the dominant phenotype and half of the recessive phenotype.
This cross can be shown by a cross for the yellow (dominant) or green (recessive) pod feature of pea plant as shown.