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
a. false. for maternal effect genes, the phenotype of the individual is determined solely by the genotype of the individual's mother. So we know Martha's mother must have been ss because Martha is sinistral. If Martha was produced as a result of self fertilization, then martha must indeed by ss. But if Martha was produced by cross fertilization, then we cannot know Martha's genotype without more information
b. True. martha's mother is ss, so Martha must be s+s or ss
c. false. because we dont know martha's genotype, we cannot predict the phenotype of her offspring
d. false. if martha is s+s then all her children will be dextral, if martha is ss then all her children will be sinistral
e. false. martha's mother's phenotype is determined by the genotype of her mother. We know Martha's mother's genotype must have been ss so her mother's mother had at least one s allele.
f, true. because Martha's mother must have been ss, all her progeny must be sinistral