24. In snails shell shape is determined by maternal genetic inheritance at a sin

Question

24. In snails shell shape is determined by maternal genetic inheritance at a single locus. The dextral (D) allele is dominant to the sinistral allele (d). You make observations about two female snails, Cynthia and her mother Nancy. You observe that Nancy has a dextral phenotype and Cynthia has a sinistral phenotype. a. (2 pts) Based upon your observations, what is/are Nancy's possible genotype(s)? b. (2 pts) If Cynthia resulted from Nancy mating with an unknown male snail observations, what is/are Cynthia's possible genotype(s)?

Explanation / Answer

A. As cynthia has sinistral phenotype this means she has both recessive allele for the trait. (dd).

It also means that one comes from father and other from the mother,so her mother must have one recessive allele and as her mother has dextral phenotype ,it means that her mother must have one dominant allele ,so her mother's genotype will be (Dd).

B. As Nancy's genotype is Dd so the gamates formed by her will be D and d .

Now if the unlnow snail has genotype DD and gmmates D and D.

So Cynthia's genotype would be

DD or Dd.

If the unknown snail her genotype Dd and gamates D and d ,then Cynthia's genotype would be either DD,Dd or dd.

If the unknow snail has genotype dd and gamates d and d then cyntCynthgenotype would be Dd or dd.

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