How many kinds of genotypes are possible in F2, if four

Solution

When four genes are segregating independently in the F2 generation, the total number of possible genotypes can be calculated by taking 2 to the power of the number of gene pairs. For each gene pair, there are 3 possible genotypes (assuming a simple dominant/recessive model - homozygous dominant, heterozygous, homozygous recessive). Therefore, the total number of genotypes for four independently segregating genes is  34 = 81 Hence, the correct answer is (2) 81.