Question

In a complementation test involving 5 monogenic recessive mutants with the same phenotype, a, b, c, d, and e, only the cross b X c produces the F1’s that do not resemble wild-type, while the F1’s from all other crosses do resemble wild-type. What conclusion is correct?

a.

These mutants represent three genes.

B.

These mutants represent two genes.

C.

These mutants represent five genes.

D.

These mutants represent four genes.

Answer 1

The Correct answer will be the option 'D' i.e. these mutants represent four genes. Complemenatation test is used to determine mutation in same gene or present in different genes. If the cross occurs between two genes like here ( a × b) the mutants will be of the phenotype similar to wildtype. It means that the mutation is present in different Genes and thus the Genes will complement each other to give the phenotype wildtype. So, a and b are two different Genes. But the cross between b and c (b × c) will produce the mutant (not wildtype phenotype). It means that the mutation is present in same Genes which don't complement each other. So, b and c are same Genes. Similarly, cross between c × d and d × e result into wildtype phenotype. So, c, d and e are different Genes. Thus, there are four different Genes, a, b or c, d and e.