Chapter 19, Problem 26P

In the 1920s, Arthur Boycott, working with the snail Limnaeaperegra, discovered the first maternal effect phenotype. Like most gastropods, the shell and internal organs of Limnaeaperegranormally coil to the right— a phenotype described as dextral. Boycott found a mutant whose body was mirror-image symmetrical to the wild type: The shell and internal body of the mutant coiled to the left—a phenotype called sinistral.

 

More recent studies have shown that sinistrality and dextrality are controlled by an autosomal maternal effect gene called s; the dominant s allele causes dextrality, and the recessive, loss-offunctions-allele causes sinistrality.

a.	Limnaeaare either hermaphrodites or males; the hermaphrodites can self-fertilize or they can mate with males. Suppose that a pure-breeding line of sinistral Limnaeahermaphrodites are crossed with males from a pure-breeding dextral line. What will be the phenotype of the progeny?
b.	Answer part (a) for a cross performed in the opposite direction: dextral hermaphrodites crossed with sinistral males.
c.	Describe the progeny phenotypes if the F1 from part (a) self-fertilize. Do the same for the F1 from part (b).
d.	Suppose you now self the F2 from parts (a) and (b). What results would you expect in the F3 in each case?