Female parent genotype =2 N=2 A Male Gamete formed =N=A Male parent genotype =2 N=4 A Male Gamete formed =N=2 A Endosperm is formed by the fusion of 2 polar nuclei (from female gamete) and 1 male gamete. Thus, the ploidy of endosperm = 3 N=A+A+2 A=4 A (tetraploid)