In 4 o'clock flowers, red is dominant to white, but the heterozygote is pink. What is the phenotype ratio of crossing red 4 o'clock flowers and pink 4 o'clock flowers?

Phenotypic ratio = 1 Red : 1 Pink

Explanation:

This phenomenon exhited by the gene coding for flower colour in four o'clock plants is called INCOMPLETE DOMINANCE i.e. the red flower allele (R) is not completely dominant over the white flower allele (r), hence, a third intermediate pink phenotype (Rr) is formed in an heterozygous state. The red and white flowers will only be expressed in a RR and rr genotypes respectively.

In a cross between a red-flowered 4 o'clock plant (RR) and a pink-flowered 4 o'clock plant (Rr), the gametes:

R and R will be produced by the red-flowered plant while gamete R and r will be produced by the pink-flowered plant. Using this gamete in a punnet square, one will have four possible offsprings in which two will be phenotypically red-flowered (RR) and two phenotypically pink-flowered (Rr). i.e. 2RR:2Rr

Hence, the phenotypic ratio is 1:1 Red to Pink flower

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