Chapter 18, Problem 4P

Flies homozygous for recessive null mutations in the sevenless (sev) or bride-of-sevenless (boss) genes have the same mutant phenotype: Every ommatidium (facet) in their eyes lacks photoreceptor cell 7 (R7). The R7 cells enable flies to detect UV light.

a.	Given that flies normally move toward light, suggest a screening method that would enable you to identify mutations in additional genes required for R7 determination
b.	Would you be able to recover mutations in every gene required for R7 development with your method? Explain.
c.	How could you tell whether any of the new mutations you found in your screen are alleles of sev or boss?
d.	Suppose you found one recessive mutant allele of a gene not previously known to be involved in eye development. How could you use this allele in a new mutagenesis screen to find additional alleles of this gene? Why might you want additional mutant alleles to study the process?