Which of the following crosses will yield four phenotypes in a ratio of 9:3:3:1?

A) RRYY × RRYY
B) RRYY × rryy
C) RrYy × RrYy
D) RrYy × rryy
E) rryy × rryy

The cross between RrYy and RrYy will yield four phenotypes in a 9:3:3:1 ratio due to the presence of two different genes that exhibit complete dominance and independent assortment. The capital "R" and "Y" alleles will result in a dominant phenotype, whereas the lowercase "r" and "y" alleles will result in a recessive phenotype. When two heterozygous individuals (RrYy) are crossed, the resulting offspring will have the following genotypes and phenotypes:

- 9/16 will be RY and display the dominant phenotype
- 3/16 will be RrYy and display the dominant phenotype
- 3/16 will be RY and display the recessive phenotype
- 1/16 will be rryy and display the recessive phenotype

Thus, the ratio of dominant to recessive phenotypes is 12:4 or 3:1, while the ratio of the two dominant phenotypes to each other is 9:3 or 3:1. None of the other crosses will yield a 9:3:3:1 phenotypic ratio.