Question

a dihybrid cross is created from plants that are heterozygous for both round seeds and yellow seed color. what is the ratio of offspring that have round seeds and yellow seed color?
○ 1:16
○ 3:16
○ 9:16
○ 16:16

Explanation:

Step1: Recall Dihybrid Cross Ratios

In a dihybrid cross with two heterozygous traits (e.g., \( RrYy \times RrYy \), where \( R \) = round, \( r \) = wrinkled, \( Y \) = yellow, \( y \) = green), the phenotypic ratio of the offspring is \( 9:3:3:1 \) for the four possible phenotypes (round - yellow, round - green, wrinkled - yellow, wrinkled - green).

Step2: Identify the Desired Phenotype

The desired phenotype here is round seeds (dominant) and yellow seed color (dominant). In the \( 9:3:3:1 \) ratio, the proportion of offspring with both dominant traits (round and yellow) is the first number in the ratio, which corresponds to \( \frac{9}{16} \) of the total offspring. So the ratio of offspring with round seeds and yellow seed color to the total is \( 9:16 \).

Answer:

C. 9:16