In summer squash, white fruit colour is governed by a dominant allele W and yellow fruit colour by its recessive allele w. A dominant allele S at another locus produced disc-shaped fruit and its recessive allele s yields sphere-shaped fruit. If a homozygous white disc variety of genotype WWSS is crossed with a homozygous yellow sphere variety wwss, the F1 are all white disk dihybrids of genotype WwSs. If the F1 is allowed to mate at random, what would be the phenotypic ratio expected in F2 generation?