The cross that will produce the most pink-flowered plants is a cross between true-breeding red-flowered plants and true-breeding white-flowered plants exhibiting incomplete dominance. In this case, the F1 generation will all have pink flowers because the red and white alleles blend to produce the intermediate pink phenotype
. More specifically:
- When a homozygous red-flowered plant (RR) is crossed with a homozygous white-flowered plant (rr), the F1 offspring are all heterozygous (Rr) and show pink flowers due to incomplete dominance, where neither allele is completely dominant over the other
- If these F1 pink-flowered plants (Rr) are self-crossed, the F2 generation will show a phenotypic ratio of approximately 1 red (RR) : 2 pink (Rr) : 1 white (rr), meaning pink flowers will be the most common phenotype in this generation
This inheritance pattern is well-documented in snapdragons and other plants where flower color shows incomplete dominance
. Thus, to produce the most pink-flowered plants, the best cross is between two pink-flowered heterozygous plants (Rr x Rr), which yields 50% pink- flowered offspring in the F2 generation, the highest proportion possible from these alleles
