Question

A third haploid pink strain (strain # 3) of yeast is isolated and known to be the MAT a sex. Nothing else is known about this strain, (i.e. we do not know whether it is a single or double mutant as we did in our lab results). When streaked together with strain #1 above the cells produced at the crossing juncture are all pink. Answer these questions:

a) Would you expect these pink cells at the strain 1-3 crossing juncture to be diploid or haploid? Why?

b) Is strain #3 mutant for ade2 (i.e. ade2) or wild type for ade2 (i.e. ADE 2). How do you know?

c) It is not clear what the genotype of strain#3 is at the ADE 1 locus.

i. What cross and result would determine that strain #3 is mutant (i.e. ade1)?

ii. What cross and result would determine that strain #3 is wild type (i.e. ADE 1)?

Answer 1

as we do not have information about which strain is #1 strain is. but i will try to answer.

ADE2 gene encodes for AIR carboxylase which catalysed purine biosynthesis pathway. mutation in this gene leads to abnormal purine biosynthesis hence the observe colonies are red. when these mutant co dominantly fused with normal wild type gene (white colony), pink colony is observed. hence,

pink colonies observed at junction of strain 1 and strain3 is diploid (both the type of gene present).

b. it is mutant for ADE2 locus, as i mentioned normal gene gives white colony and mutant gene will gives dark red color colony which co dominantly gives pink colony when crossed with white normal colony.

c.

i. when you cross strain 3 is with wild mutant ADE1 it will gives red colony which means the strain is mutant.

ii. if we cross strain 3 with wild type ADE1 it will gives normal colony of white cells which means the locus is wild type.

as the information is not completed i will just assume the result.