Please Help with this genetics question Please explain your

Please Help with this genetics question. Please explain your answer. I under stand that a canavine screen/plate is used to test for mutations where it provides faulty canavine instead of the amino acid arginie.

15) A week ago I plated 3 strains of yeast on four different plates (one YPD plate and three SC plates), by themselves. Below is a table showing my results. A means that the strain grew on the indicated plate. A means that the strain failed to grow on the indicated plate. Use this table to answer questions 15 17 Strain YPD SC adenine SC tryptophan SC canavanine Which mutations, if any, does Strain 1 have? (Select all that apply) A) Arginine permease mutant. B) Auxotrophic for adenine. C) Auxotrophic for canavanine. D) Auxotrophic for tryptophan. E) No mutations detected 16 Which mutations, if any, does Strain 2have? (Select all that apply. A) Arginine permease mutant. B) Auxotrophic for adenine. C) Auxotrophic for canavanine. D) Auxotrophic for tryptophan. E) No mutations detected 17) Which mutations, if any, does Strain 3have? (Select all that apply. A) Arginine permease mutant. B) Auxotrophic for adenine. C) Auxotrophic for canavanine. D) Auxotrophic for tryptophan. E) No mutations detected

Solution

Answers:

15. (E) No mutations detected.

The yeast strain grows in all plates except SC+canavanine. When wild type yeast cells are plated on a plate with canavanine, the cells will die from protein translation errors caused by canavanine taking the place of arginine. So, its the WT strain.

16. (B) and (D) Auxotrophic for both adenine and tryptophan.

Since it is adenine and trp auxotroph, it cannot grow in media lacking adenine and tryp. But, it is not a arginine permease mutant since it can take up canavanine from the SC+canavanine media. This results in incorporation of canavanine in place of arginine in the protein, and thus no growth on the SC+canavanine.

17. (A) Arginine permease mutant

Arginine permease helps in the import of arg from the media into the cells. If the arginine permease is non functional, it will not allow import of canavanine. Thus, no canavanine will get imported from the media and the cells can grow on the SC+canavanine plate, since no canavanine gets incorporated into the protein.