How many different diploid genotypes are possible for a gene that exists in seven allelic forms? Solution Ans. Given, Ploidy = diploid Number of alleles of gene = n = 7 For a diploid organism, number of genotypes = [ (n) (n+1) ] / 2 Where, n = number of alleles Or, number of genotypes = [7 x (7+1)] / 2 = 28 Also, Number of genotypes = sum of all number from n to 1 = (7 + 6+ 5+ 4+ 3+ 2+ 1) = 28.