Solutions For An Introduction to Genetic Analysis Chapter 6 Problem 31P

The yeast geneticist irradiates haploid cells of a strain that is an adenine-requiring auxotrophic mutant by mutation of the gene ade1 and showed his results. From those results,

a) The first result where the cross gets all prototrophic strains is because of the reversal of original ade1 mutant to wild type strain. But in the case of the second result where a 3:1 ration was observed was due to the fact that a new mutation (say for example sup^m) is an unlinked gene that suppresses the activity of ade1^- phenotype.

The cross between the prototroph and the wild type giving a 3:1 ratio would be obtained as follows:

ade1 ^-; sup^m X ade1⁺; sup

Progeny will be as follows:

¼ ade1⁺; sup prototroph

¼ ade1⁺; sup^m prototroph

¼ ade1^-; sup^m prototroph

¼ ade1^-; sup auxotroph