Chapter 19, Problem 28P

Some genes are required both zygotically and maternally. One experimental approach to studying such genes relies on the existence of ovo^D , a dominant female sterile mutation of the ovo gene, which is located near the middle of the acrocentric Drosophila X chromosome. Females that are ovo^D /ovo⁺ are sterile; ovo^D>–containing germ-line cells cannot produce eggs.

a.	Mutations in gene X are recessive lethals, so homozygotes for these mutations do not develop into adults. Explain how researchers could use the ovoD mutation in a mitotic recombination experiment to determine (i) whether or not females might supply the RNA or protein product of gene X to the eggs they make in their ovaries, and (ii) whether this maternally supplied product is needed for proper development of their progeny. Where in the genome would gene X need to be located for this approach to work?
b.	The ovoD mutant gene has been cloned, so genomic DNA for this mutant gene is available. How could you use this cloned DNA to determine whether any embryonic lethal mutation located anywhere in the genome was an allele of a maternal effect gene?
c.	Regardless of its chromosomal location, how could you distinguish in such an experiment whether the gene in question was a maternal effect gene, as opposed to a gene whose product is needed for oogenesis in the female?
d.	How can fly strains containing ovoD mutations be maintained if females carrying these mutations are sterile?