Part B

A synthetic lethal interaction is one in which two yeast stains
with non-lethal phenotypes are crossed and the resulting double
mutant is lethal.

Of these yeast strains, what are all the possible
combinations that could be crossed to look for synthetic lethal
interactions?

Strain A: a null mutation in a nonessential
gene
Strain B: a null mutation in an essential
gene
Strain C: a conditional mutation in an essential
gene

(B) Yeast cells with a null mutation in an essential
gene cannot survive.

(C) However, if the mutation in the essential gene is
conditional (meaning that the phenotype only shows under certain
conditions), the cell can survive under normal
conditions.

(A) Additionally, cells with null mutations in
nonessential genes can survive because the nonessential genes are
not required for survival.

Select all that apply.