Download Mutations responsible for regulatory network differences

 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: 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
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