Question

A certain kind of snail can have a right-handed direction of shell coiling (dd or dd) or left-handed coiling (dd). however, if direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s) and phenotype(s)?

Answer 1

I believe that The offspring genotype will be ; 1/2 Dd : 1/2dd
And the phenotype will be that half right and half left coiling.
This is because the right-handed direction of coiling is dominant over the left handed coiling, which means the right handed coiling phenotype will be observed for both homozygous genotype DD and heterozygous genotype dd, Therefore a cross between heterozygous Dd and homozygous for left coiling will yield half of the offspring being right coiling and the other half being left coiling.

Answer 2

A certain kind of snail can have a right-handed direction of shell coiling (DD or Dd) or left-handed coiling (dd). However, if direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s) and phenotype(s)?

A. all Dd; half right-coiling and half left-coiling

B. all Dd; all right-coiling

C. 1/2 Dd:1/2 dd; all right-coiling

D. 1/2 Dd:1/2 dd; half right-coiling and half left-coiling

Answer:

D. 1/2 Dd:1/2 dd; half right-coiling and half left-coiling

Explanation:

right-handed direction of shell coiling (DD or Dd)

left-handed coiling (dd)

If a Dd egg-producing snail and a dd sperm-producing snail breeds together, we will have the following type of offspring

Dd × dd = ( Dd, Dd, dd, dd )

Genotype = 2/4 =1/2 (Dd, dd)

Phenotype = 2/4 =1/2  (Dd, dd)

Thus , option D is the right answer , (1/2 Dd:1/2 dd; half right-coiling and half left-coiling)