This tutorial will take you step-by-step through Step 4: Identify the evidence from a pedigree that can be the question. used to determine an individual's genotype in a genetic system with a maternal effect, and determine an Shell coiling of the snail Lymnaea peregra results from a individual's genotype from this evidence. 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 Which pieces of information can be used to determine females. However, a pet snail named Martha is sinistral and Martha's genotype? reproduces only as a female. Martha and her family are Martha's progeny have dextral shells. shown in the pedigree. Martha's mom's genotype is ss. Martha's mom has a dextral shell. Martha's dad has a sinistral shell. There is not enough information to determine Martha's genotype. What is Martha's genotype? s + s s + s + ss unknown.