Final answer:
The phenotypic ratio for Mendel's F2 cross, when two heterozygous individuals are crossed, is 3:1 for dominant to recessive traits. This is due to the combinations of genotypes possible in the offspring, where three out of four express the dominant phenotype.
Step-by-step explanation:
Phenotypic Ratio for Mendel's F2 Cross: When two heterozygous individuals are crossed in Mendel's experiments, the phenotypic ratio observed in the F2 generation is a 3:1 ratio of dominant to recessive traits. The reasoning behind this is based on the Punnett square of a monohybrid cross, which shows that when both parents contribute heterozygous genes (Bb), the offspring will potentially have one of four genetic combinations: BB, Bb, Bb, or bb.Since there are two ways to obtain a Bb genotype and the phenotypic expression of a dominant trait does not distinguish between homozygous dominant (BB) and heterozygous (Bb) genotypes, the expected outcome is that three quarters of the offspring will express the dominant phenotype and one quarter will express the recessive phenotype, hence the 3:1 phenotypic ratio.To conclude, the correct answer to what is the phenotypic ratio for Mendel's F2 cross when two heterozygous individuals are mated is B) 3:1.