Question

Suppose we have one true-breeding strain of tomato that produces red fruit. Suppose we also have a true-breeding strain of tomato that produces yellow fruit. We KNOW that a single gene is responsible for fruit color, and that the red allele is dominant to the yellow allele. If you make an F2 cross, what proportion of those fruits would you expect to be yellow

Answer 1

Answer:

1/4 or 25%

Explanation:

Let us assume that the fruit color trait in the tomato is represented by R and r. The dominant color red would be represented by R while the recessive color yellow would r.

If a true-breeding red fruit tomato (RR) is crossed with a true-breeding yellow fruit tomato (rr), the F1 would be thus:

             RR    x    rr

          Rr   Rr   Rr   Rr

Since R is dominant over r, all the F1 offspring would produce red fruits with the genotype Rr.

At F2:

               Rr    x    Rr

           RR   Rr   Rr   rr

RR and Rr = red

rr = yellow

Hence, the proportion of the F2 offspring expected to be yellow would be 1/4 or 25%.