Chapter 8, Problem 42P

Null mutations are valuable genetic resources because they allow a researcher to determine what happens to an organism in the complete absence of a particular protein. However, it is often not a trivial matter to determine whether a mutation represents the null state of the gene.

a.

Geneticists sometimes use the following test for the nullness of an allele in a diploid organism: If the abnormal phenotype seen in a homozygote for the allele is identical to that seen in a heterozygote (where one chromosome carries the allele in question and the homologous chromosome is known to be completely deleted for the gene) then the allele is null. What is the underlying rationale for this test? What limitations might there be in interpreting such a result?

b.

Can you think of other methods to determine whether an allele represents the null state of a particular gene?