Question

Supposing shell color in scallops is controlled by a single gene. Using appropriate symbols that you specify, please explain the following results by providing four Punnett Squares. Give a short explanation of your logic as needed.

a. yellow shells X black shells produce ½ yellow offspring + ½ black offspring

b. black shells X black shells produce 100% black offspring

c. orange shells X orange shells produce ¾ orange offspring + ¼ black offspring

d. yellow shells X orange shells produce ¼ orange with yellow spots + ¼ orange + ¼ yellow + ¼ black.

Answer 1

To solve this question, one has to consider that the gene is controlled by multiple alleles like the gene controlling the blood group in humans. Also, Yellow and Orange are codominant, and black is the recessive allele.

Representing the shell colors as:

Yellow: IAIA  or  IAi

Orange:IBIB or IBi

Black: ii

a. yellow shells X black shells produce ½ yellow offspring + ½ black offspring

IAi X     ii   

b. black shells X black shells produce 100% black offspring

ii X ii

c. orange shells X orange shells produce ¾ orange offspring + ¼ black offspring

IBi X   IBi

d. yellow shells X orange shells produce ¼ orange with yellow spots + ¼ orange + ¼ yellow + ¼ black.

IAi X IBi

Taking these genotypes gives the required result, Hence it is confirmed that the genotypes taken are correct.

In case of codominance, both the alleles of a gene are expressed without being mixed. Like in this question, both Yellow and orange genes are expressed when mating two orange scallops gives 1/4th of a progeny as orange with yellow spots. Both the colors are expressed simultaneously without getting mixed.

I hope you got the answer.