Mating in yeast

1. Mating in yeast • Stressed diploid yeast undergoes meiosis • Haploid daughters are either… • “a” cells or • “a” cells • A-cells and a-cells mate • Only a-cell with a-cell • Attracted by pheromones • Produce new diploid cell From http://en.wikipedia.org/wiki/Image:Yeast_Mating.png. © 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458

2. The regulation of mating type • Distantly related yeast exhibit same differentiation of haploid mating types • But use different regulatory elements From Figure 1 in Rokas, A. (2006) “Different paths to the same end” Nature 443: 401-402. © 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458

3. Mutations responsible for regulatory network differences • Small number of mutations can have big impact on gene regulation • Example: Mcm1 – a2 protein interaction • Mutations in small region of a2 protein account for absence of repression of asgs in some yeast species From Figure 5 in Tsong, A. et al. (2006) “Evolution of alternative transcriptional circuits with identical logic” Nature 443: 415-420. © 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458

4. Evolutionary transitions in the regulatory network • Comparison of regulatory networks governing yeast mating type suggests… • big changes in genotype without… • concurrent changes in phenotype • However it is possible that there was selective advantage in different regulatory networks despite identical mating type outcome © 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458