Stressed diploid yeast undergoes meiosis Haploid daughters are

· 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. Mating in yeast © 2005 Prentice Hall Inc. / A Pearson Education Company / Upper Saddle River, New Jersey 07458

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

Mutations responsible for regulatory network differences · Small number of mutations can have big impact on gene regulation · Example: Mcm 1 – a 2 protein interaction · Mutations in small region of a 2 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

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