Question

Given that you have isolated 8 mutants in yeast that fail to grow on a 3 carbon source such as glycerol but do grow when they are supplemented with a 6 carbon food source such as glucose. You know that glycerol can be used in a biochemical pathway within wild-type yeast, but you do not know how many gene products it takes for the pathway. You have all of the lines as both a and a cells and mate each strain to each other in pairwise crosses and plate them on minimal media to see if they grow. You obtain the following results with (+) representing growth, and (-) indicating no growth:

1 2 3 4 5 6 7 8

1 - + + - - + + +

2 + - + + - + + -

3 + + - + - + + +

4 - + + - - + + +

5 - - - - - - + -

6 + + + + - - + +

7 + + + + + + - +

8 + - + + - + + -

Answer 1

The student is applying a complementation test to determine the genetic basis for yeast mutants' inability to grow on glycerol. The mating results suggest which mutants may have mutations in the same or different genes, which helps infer the number of genes involved in the glycerol pathway.

Step-by-step explanation:

The question involves using complementation tests with isolated 8 mutants of yeast to understand the genetic basis for their inability to grow on a three-carbon source like glycerol, compared to a six-carbon source like glucose. This kind of experiment is rooted in classical genetics and has been an effective strategy for understanding metabolic pathways and genetic interactions. Researchers such as Francois Jacob and Jacques Monod used similar complementation testing to understand the growth of E. coli on different carbon sources. Complementation tests help determine whether mutations occur in the same gene (they don't complement) or in different genes (they do complement). When you mate two haploid yeast strains, each carrying different mutations, and the diploid offspring can grow on minimal media, this indicates that the mutations are in different genes, as one functional copy of each gene is enough to restore the pathway. In the results presented, the growth (+) or no growth (-) patterns on minimal media indicate which mutants have mutations in the same or different genes, allowing inference of the number of gene products involved in the pathway that allows growth on glycerol.