Nconsidering the cross yyrr x yyrr, the phenotype ratios of the f2 generation will be 1: 3: 1 3: 1 9: 3: 3: 1 4: 1

The cross of YyRr will produce 16 distinct genotypes.

If the two alleles are far enough on the same chromosome, then the Y and R alleles will be distributed independently of one another, so that the genotypic ratio among each allele would be 1:2:1 (YY:Yy:yy, and similarly for the R allele). Then the dihybrid cross will yield a genotypic ratio of 1:2:1:2:4:2:1:2:1 (YYRR:YYRr:YYrr:YyRR:YyRr:Yyrr:yyRR:yyRr:yyrr).

Now, assuming perfect Mendelian inheritance (complete dominance), the phenotypes exhibited by YY and Yy will be considered equivalent, and similarly for RR and Rr, so the phenotypic ratio would be 9:3:3:1 (YR:Yr:yR:yr).

The answer to that is 6