Explanation : Tallness is a dominating trait and can be expressed in homozygous as well as heterozygous condition also while recessive traits (in pea) are expressed only in homozygous condition. So, to find out the genotype of the tall pea with white plant we will test cross it with a dwarf pea plant bearing white flowers (as it is homozygous). If the progeny shows 1 : 1 ratio between dominating and recessive trait, i.e.,50% progenies are tall with white flowers and 50% are dwarf with white flowers then this proves the experimental plant is heterozygous for the dominating trait. And if all the progenies i.e., 100% plants are tall with white flowers, thus this proves that the experimental plant (Tall with white flower) was homozygous for tallness or the dominant trait. The type of the cross is the test cross as shown above.