A male Drosophila melanogaster has the genotype Aa Bb Cc XDY

A male Drosophila melanogaster has the genotype A/a; B/b; C/c; XD/Y. How many different sperm genotypes can it produce through meiosis of one single pre-gametic (2n) cell?

The answer is 16 but i dont understand how to get to that answer. Can someone explain?

Solution

16 different gametes are produced.

Formula-2^n

n is the number of heterozygous pairs =4