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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
• The work highlighted in the Nova piece on
Katie Pollard fits nicely with earlier studies
comparing gene expression patterns in human
and chimp.
2002: Gene expression differences weren’t that
different in non-brain tissues…
Gene activity, not sequence,
“makes us human”
Enard et al., Science, 2002, 296: 340-343
2003: Gene expression in human and chimp
cerebral cortex …
Red = increased expression
169 different genes with expression differences between human and chimp in cortex
Most genes were more highly expressed in human vs. chimp
Caceres et al., 2003, PNAS, 100: 13030-13035
Katie Pollard’s work implicates the “switches” as the
genetic mechanism behind the gene expression
differences
Prx1
Prx1 is naturally
expressed at
different levels in
bat and mouse
during limb
development
Created knock-in
mice (replaced
mouse switch with
bat switch for
Prx1). Limb length
was increased 6%
(sig)
Cretekos et al., 2008, Genes and
Development
• Sean Carroll, “switches” and fly wing spots
(gene expression is turned on by particular sequence)
A glimpse of the actual wing trans-regulatory landscape.
Prud'homme B et al. PNAS 2007;104:8605-8612
©2007 by National Academy of Sciences
Prud'homme B et al. PNAS 2007;104:8605-8612
©2007 by National Academy of Sciences
Body-plan evolution by compounding regulatory changes.
Prud'homme B et al. PNAS 2007;104:8605-8612
©2007 by National Academy of Sciences
Schematic comparison of Hoxc8 expression in chicken and mouse in relationship to
morphological landmarks.
Belting H et al. PNAS 1998;95:2355-2360
©1998 by The National Academy of Sciences
Hoxc8 figure from Time Mag.
Examples involving
gene duplication
• Can arise by unequal crossing over (gene
duplication)
• Can arise by genome duplication (failure of
meiosis to produce haploid gamete)
Is it common?
• Several hundred duplicated genes every
million years in Drosophila
Gene Duplications
• Especially important in evolution…
– Can change protein quantity (e.g., human amylase)
– Duplicated gene may take on a new job if mutation
alters it
– Duplicated gene may be expressed at a different
time or location if “switch” sequence is altered
Gene Duplication seems to be more common in
our lineage than in other primate lineages
Marques-Bonet et al., Nature, Feb. 12, 2009
Gene duplication seems especially common in the human lineage even
compared to the chimp/bonobo lineage… does this account for gene
expression diffferences we discussed earlier?
Marques-Bonet et al., Nature, Feb. 12, 2009
Color vision is useful…
http://www.neitzvision.com/content/home.html
Color vision in Old World Primates (including
humans) is trichromatic
Jacobs and Nathans, Scientific American, April 2009
Red and green genes are very similar and are likely due to
a duplication event (unequal crossover) and gene cooption
Jacobs and Nathans, Scientific American, April 2009
Both males and females are
trichromatic…
Jacobs and Nathans, Scientific American, April 2009