Question

In garden peas, long stems are dominant to short stems, and yellow seeds are dominants to green seeds, too long/yellow pea plants, all of which had one short/green parent, are interbred (bred to each other). 1600 progeny result. Please answer the following questions about the progeny.
A. Assuming that these two genes are unlike, about how many long/green pea plants would you except to find among the offspring?
B. What ratio of yellow to green seed color would you expect among the offspring?
C. What would you expect the overall phenotypic ratio among the 1600 offspring to be (taking into consideration both traits)?

Answer 1

Answer:

A) 300

B) 3:1

C) 9 long yellow : 3 long green : 3 short yellow : 1 short green

Explanation:

Long stems (L_) are dominant to short stems (ll)

Yellow seeds (Y_) are dominant to green seeds (yy)

We interbred pea plants with long stems and yellow seeds (L_Y_), but they had a short green parent (llyy) that could have only produced ly gametes, so our plants are heterozygous LlYy.

C) We interbred them LlYy x LlYy. If the two genes are unlinked, this is a typical dihybrid cross and from Mendel's law of independent assortment we know that the offspring will have the following phenotypic ratios:

• 9/16 L_Y_ (Long, yellow)
• 3/16 L_yy (Long, green)
• 3/16 llY_ (short, yellow)
• 1/16 llyy (short, green)

A) 3/16 × 1600 = 300 plants will be long and green.

B)

9/16 + 3/16 = 12/16= 3/4 plants will be yellow;

3/16 + 1/16 = 4/16= 1/4 plants will be green.

The ratio will be 3 yellow : 1 green