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I am studying the metabolism of galactose in the budding yeast Saccharomyces cerevisiae. After a random mutagenesis screen, several mutant strains were isolated that grow well in glucose but are unable to grow when the only carbon source in the plate is galactose. Two mutants have already been characterised and they carry point mutations in the genes GAL1 and GAL10. A third mutant, galx, needs to be characterised.

which type of genetic cross would I need to perform to prove that the phenotype (i.e. no growth on galactose containing plates) is due to a mutation on a single gene (GALx)?

My thoughts are to carry out a genetic cross between halpoids of yeast with a wild type to produce a diploid offspring which is heterozygous wild type. The ratio of its offspring would be 1:1 due to haploids being formed and this will show the phenotype is due to a single gene. Is this an ok method?

ALSO, how can I use a genetic test to determine that GALx is not one of the genes already characterised (i.e. GAL1 and GAL10)?

I suggest doing a complementation test...would that work?

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  • $\begingroup$ Hello! Your post is well phrased, but it seems to be a homework question for me, that is off topic unless you share your own findings. If it is indeed a homework question please share your results to avoid closure. $\endgroup$ – Nandor Poka Jun 26 '15 at 11:18
  • $\begingroup$ There are two mutually exclusive outcomes from a genetic complementation test. Either the two alleles complement so that the heterozygous cross-progeny are wild-type phenotype, OR, the heterozygous cross-progeny exhibit the mutant phenotype and therefore the two alleles fail to complement each other. If you understand my second sentence then you don't need to ask us your final question. N.B. to be interpretable a complementation test can only be carried out with recessive alleles. $\endgroup$ – mdperry Jun 27 '15 at 0:10

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