Shell coiling of the snail Lymnaea peregra results from a genetic maternal effec

Question

Shell coiling of the snail Lymnaea peregra results from a genetic maternal effect. An autosomal allele for a right-handed shell, s^+, called dextral, is dominant over the allele for a left-handed shell, s, called sinistral. In general, snails are hermaphroditic and reproduce as both males and females. However, a pet snail named Martha is sinistral and reproduces only as a female.

Martha's dad Martha's mom Sinistral DextralMartha Dextral Sinistral Sinistral Sinistral Sinistral Sinistral Sinistral Dextral Dextral Dextral From the pedigree above, determine Martha's, her mother's, and her father's genotypes. Place the genotype next to the individuals listed below the pedigree Martha's genotype Martha's mom's genotype Continued below unknown s S Martha's dad's genotype

Explanation / Answer

Sinistral = recessive = ss = left handed shell

Dextral = Dominant = s+s+ or s+s = Right handed shell

Martha:

Phenotype: Sinistral

So, she has to be recessive at both the loci.

Genotype = ss

Martha's mother:

Phenotype: Dextral

She produces Martha who is sinistral. So, she must contain at least one sinistral allele.

But, her phenotype is dextral. So, she also must contain at least one s+ allele.

Genotype = s+s

Martha's father:

Phenotype: Sinistral

So, she has to be recessive at both the loci.

Genotype = ss

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