Discussion:
Strain of Aspergillus was subjected to mutagenesis by X rays
A strain of Aspergillus was subjected to mutagenesis by X rays, and two tryptophan-requiring mutants ( A and B) were isolated. These tryptophan-requiring strains were plated in large numbers to obtain revertants to wild type. You failed to recover any revertants from mutants A and recovered one revertant from mutant B. This revertant was crossed with a normal wild-type strain. What proportion of the progeny from this cross would be wild type if
a) the reversion precisely reversed the original change that produced the typ- mutant allele?
b) the revertant phenotype was produced by a mutation in a second gene located on a different chromosome (the new mutation suppresses trp-)?
Propose an explanation of why no revertants from mutant A were recovered.