Question

in a dihybrid cross involving pea plants heterozygous for two traits (rryy × rryy), how many of the offspring will be phenotypically yellow? round (r) is dominant over wrinkled (r), and yellow (y) is dominant over green (y). a 12/16 b 9/16 c 4/16 d 3/16

Explanation:

Step1: Analyze the cross for each trait separately

For the seed shape trait (\(Rr\times Rr\)):

• Using the Punnett - square or the formula for a monohybrid cross (\(Aa\times Aa\)), the phenotypic ratio is \(3\) (dominant, \(R-\)):\(1\) (recessive, \(rr\)).

For the seed color trait (\(Yy\times Yy\)):

• Using the Punnett - square or the formula for a monohybrid cross (\(Aa\times Aa\)), the phenotypic ratio is \(3\) (dominant, \(Y-\)):\(1\) (recessive, \(yy\)).

Step2: Use the multiplication rule for independent events

We want to find the proportion of offspring that are yellow (\(Y-\)). Since the inheritance of seed - shape and seed - color traits are independent (Mendel's law of independent assortment), we only consider the seed - color part of the cross.
The cross for seed color is \(Yy\times Yy\). The probability of getting a yellow - seeded plant (\(Y-\)) is \(\frac{3}{4}\) (because \(YY:Yy:yy = 1:2:1\), and \(YY + Yy\) gives the yellow phenotype).

Step3: Convert the fraction to sixteenths

To convert \(\frac{3}{4}\) to a fraction with a denominator of \(16\), we use the formula \(\frac{3}{4}=\frac{3\times4}{4\times4}=\frac{12}{16}\)

Answer:

A. \(12/16\)