Question

In order to study the lysine biosynthetic pathway in yeast, lysine auxotrophs(mutants that are unable to grow without lysine supplementation to the minimal growth medium) were screened. Four mutants(m$1$ to m$4$) were isolated, which were all recessive compared to the wild-type(WT). To find out the number of genes affected by these mutations, haploid mutants were mated and the ability of the resultant diploid progeny to grow on medium lacking lysine was tested. The results are shown in the table.
(${}^{\prime }{+}^{\prime }$ indicates growth and ${}^{\prime }{-}^{\prime }$ indicates no growth) Based on these results, which of the following statement(s) is/are correct?

• A. There are three genes affected by the mutations
• B. m$1$ and m$3$ are mutations on the same gene
• C. m$2$ and m$4$ are likely to display the same phenotypic defect
• D. m$1$ and m$2$ are mutations on different genes

Answer 1

Answer: (B), (C), (D)

The correct options are
B m$1$ and m$3$ are mutations on the same gene
C m$2$ and m$4$ are likely to display the same phenotypic defect
D m$1$ and m$2$ are mutations on different genes

From the results shown in the table, the mutations affect two genes. Mutants m1 and m3 shows the same defect and thus, they are the mutations on the same gene. Mutants m2 and m4 have mutations which show similar phenotypic defect. Mutants m1 and m2 show completely different effects and thus, they are the mutations on different genes.

Thus, the correct answer are options B, C and D.