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Class Discussion
Syphilis tree papers
Your phylogenetic tree papers
Mutation/selection examples involving
change in protein shape
Mc1r gene in Rock Mice
Dark/light color varies by location
Kaufman, 1974
Conspicuous mice captured more
frequently than cryptic mice
Unusual color for the species
Nachman et al., 2003, PNAS, 100: 5268
Mc1r gene in Rock Mice
Mc1r
some other gene
“Different molecular solutions to arrive at the same
phenotype in similar environments”
Nachman et al., 2003, PNAS, 100: 5268
Mc1r gene in Beach Mice
Unusual color for the species
Steiner et al., Molecular Biology and Evolution, 26:35-45.
Experimental steps...
1. Documented phenotypic convergence in Gulf
coast and Atlantic coast subspecies
2. Determined relationships among Gulf coast
and Atlantic coast subspecies compared with
inland mice
3.Sequenced the Mc1r coding region in all mice
It was already demonstrated that in some beach mice, a point mutation in
gene sequence changes Arg  Cys, which alters both ligand binding
and receptor-signaling potentials consistent with light pigmentation
I.e., Change in protein shape
Steiner et al., Molecular Biology and Evolution, 26:35-45.
Beach mouse phylogeny
mtDNA sequences + snp’s
Light color arose > 1 time
Steiner et al., Molecular Biology and Evolution, 26:35-45.
Mc1r gene tree
mtDNA sequences + snp’s
“Different molecular solutions to arrive
at the same phenotype in similar
environments”
Other light colored
mice (color not due to
same mutation)
A point mutation in
gene sequence changes
Arg  Cys
Steiner et al., Molecular Biology and Evolution, 26:35-45.
We’ve seen this convergence in phenotype from
different genetic mechanisms before…
e.g., convergent loss of pigment in cave
fish populations is caused by
independently derived mutations that
prevents the Oca2 gene from
producing a functional protein
(LOF mutations)
Protas et al., 2006, Nature Genetics
Mutation examples involving switches
• What Darwin never knew (switches) video
• http://www.pbs.org/wgbh/nova/evolution/d
arwin-never-knew.html
• Watch 1:44:00 to 1:49:15