Question

Shell coiling of the snail Limnaea peregra results from a genetic maternal effect. An autosomal allele for a right handed shell (s+) called dextral, is dominant over the allele for the left handed shell (s) called sinistral. A pet snail called Martha is sinistral and reproduces only as a female.

True or false...
a. martha's genotype must be ss
b. martha's genotype cannot be s+s+
c. all the offspring produced by martha must be sinistral
d. at least some of the offspring produced by Martha must be sinistral
e. Martha's mother must have been sinistral
f. all Martha's brothers must be sinistral

Answer 1

Martha's genotype must be ss. Martha's genotype cannot be s+s+. All the offspring produced by Martha must be sinistral.

Step-by-step explanation:

The genotype of Martha, the sinistral snail, can be determined based on the given information. Since the allele for sinistral shell (s) is recessive to the allele for dextral shell (s+), Martha must have two copies of the recessive allele, which makes her genotype ss. Therefore, option a is true.

As for option b, Martha's genotype cannot be s+s+ because the allele for sinistral shell is recessive and Martha is sinistral, indicating that she does not possess the dominant allele. Therefore, option b is false.

Regarding option c, since Martha is sinistral (ss), she can only pass on the recessive allele for sinistral shell to her offspring. Therefore, all of Martha's offspring must be sinistral. Hence, option c is true.

Option d is also true because some of Martha's offspring may inherit the sinistral allele from her and therefore be sinistral.

Option e cannot be determined from the information provided. Martha's mother could have been sinistral or dextral since her shell coiling phenotype is not specified.

Lastly, the shell coiling phenotype of Martha's brothers cannot be determined. It depends on the genotypes of Martha's parents and the inheritance of the shell coiling alleles. Therefore, option f cannot be determined.