Yeast are single-celled eukaryotic organisms that grow in
culture as either haploids or diploids. Diploid yeast are generated
when two haploid strains fuse together. Seven haploid strains of
yeast exhibit similar growth habit: at 25 ∘C, each strain grows
normally, but at 37 ∘C, they show different growth capabilities.
The table below displays the growth pattern.

Part A

Describe the nature of the mutation affecting each of these
mutant yeast strains. Explain why stains B and G display different
growth habit at 37 ∘C than the other stains.

Each of the mutant pairs of haploid yeast is fused, and the
resulting diploids are tested for their ability to grow at 37 ∘C.
The results of the growth experiment are shown below.

How many different genes are mutated among these seven yeast
strains?

Please try to explain the reasoning.