Question
Explain what would be the ratio of the pure red and the pure white flower-bearing pea plants in the F2 generation, when a cross is made between two pea plants, one bearing pure red flower (dominant) and the other bearing pure white flower (recessive).
Answer
When a cross is made between two pea plants, one bearing pure red flower (dominant) and the other bearing pure white flower (recessive), the F1 generation will all have a red flower phenotype as it is dominant over the white flower. However, they will be heterozygous (Rr) as they have inherited one dominant red allele (R) and one recessive white allele (r) from their parents.
When the F1 generation is self-crossed, the resulting F2 generation will exhibit a phenotypic ratio of 3:1 for red to white flowers. This is because the heterozygous F1 plants can produce two types of gametes, one carrying the dominant red allele (R) and the other carrying the recessive white allele (r), in equal proportions. When these gametes combine randomly in fertilization, they can give rise to three possible genotypes: RR (pure red), Rr (red), and rr (pure white) in a ratio of 1:2:1. Hence, the resulting phenotypic ratio of the F2 generation will be 3:1 for red to white flowers.
