You Are Studying a Diploid Yeast Strain That Normally Uses

You are studying a diploid yeast strain that normally uses glucose as an energy source but can use maltose when no glucose is present.You are interested in understanding how this yeast strain metabolizes maltose as an alternative energy source.You isolate the genes involved in maltose metabolism by screening for yeast that cannot grow when maltose is the sole energy source.You find six different mutants, all of which are recessive, and name these alleles mal1, mal2, mal3, mal4, mal5, and mal6.Next, you isolate gametes from the homozygous diploid mutant yeast strains and perform crosses between the different strains to do complementation analysis, because you wish to determine whether the mutations are likely to affect the same or different genes.Your results are shown in Table 19-20. $\begin{array}{ccccccc}\text { mutation } & \text { mal1 } & \text { mal2 } & \text { mal3 } & \text { mal4 } & \text { mal5 } & \text { mal6 } \\\hline \text { mal1 } & - & - & + & + & + & - \\\text { mal2 } & - & - & + & + & + & - \\\text { mal3 } & + & + & - & + & - & + \\\text { mal4 } & + & + & + & - & + & + \\\text { mal5 } & + & + & - & + & - & + \\\text { mal6 } & - & - & + & + & + & -\end{array}$

" $+$ " $=$ growth on maltose-containing media;
$" -" =$ no growth on maltose-containing media
Table 19-20
In how many genes are you likely to have isolated mutations? Which alleles seem to affect the same genes? Explain your answer.