When flowers known as "four-o'clock" are crossed, there is an incomplete dominance. A four-o'clock is red if the genotype is rr and white if it is ww. If rr is crossed with ww, a hybrid rw results. Suppose a population of 50% red four-o'clocks is mixed with a population of 50% white four-o'clocks. What percent of the population has each phenotype?

Question

When flowers known as "four-o'clock" are crossed, there is an incomplete dominance. A four-o'clock is red if the genotype is rr and white if it is ww. If rr is crossed with ww, a hybrid rw results. Suppose a population of 50% red four-o'clocks is mixed with a population of 50% white four-o'clocks. What percent of the population has each phenotype? ​

Quizplus · Accepted Answer

Since the four-o'clock flower displays incomplete dominance, the heterozygous offspring (rw) will show a blend of the two parental phenotypes, resulting in a pink flower. Therefore, the genotypic ratio from the cross (rr x ww) is 100% Rw. When 50% of the population is red (rr) and 50% is white (ww), this means that the initial population is homozygous for either allele. Therefore, the genotypic ratio for the entire population is 50% rr and 50% ww. Combining this information, we can use a Punnett square to find the phenotypic ratio of the offspring:
             r        w
r         Rr       Rw
w         Rw       ww
There are two Rw individuals, which will display the pink phenotype, giving us a phenotypic ratio of 25% red, 50% pink, and 25% white. Therefore, the correct answer is choice C.

When Flowers Known as "Four-O'clock" Are Crossed, There Is an Incomplete