mutation examples involving switches. what darwin never knew (switches) video arwin-never-knew.html
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Mutation examples involving switches
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• 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
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• The work highlighted in the Nova piece on Katie Pollard fits nicely with earlier studies comparing gene expression patterns in human and chimp.
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2002: Gene expression differences weren’t that different in non-brain tissues…
Enard et al., Science, 2002, 296: 340-343
Gene activity, not sequence, “makes us human”
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2003: Gene expression in human and chimp cerebral cortex …
Caceres et al., 2003, PNAS, 100: 13030-13035
Red = increased expression169 different genes with expression differences between human and chimp in cortexMost genes were more highly expressed in human vs. chimp
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Katie Pollard’s work implicates the “switches” as the genetic mechanism behind the gene expression differences
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Prx1
Cretekos et al., 2008, Genes and Development
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)
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• Sean Carroll, “switches” and fly wing spots (gene expression is turned on by particular sequence)
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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
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Prud'homme B et al. PNAS 2007;104:8605-8612
©2007 by National Academy of Sciences
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Body-plan evolution by compounding regulatory changes.
Prud'homme B et al. PNAS 2007;104:8605-8612
©2007 by National Academy of Sciences
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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
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Hoxc8 figure from Time Mag.
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Examples involving gene duplication
• Can arise by unequal crossing over (gene duplication)
• Can arise by genome duplication (failure of meiosis to produce haploid gamete)
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Is it common?
• Several hundred duplicated genes every million years in Drosophila
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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
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Marques-Bonet et al., Nature, Feb. 12, 2009
Gene Duplication seems to be more common in our lineage than in other primate lineages
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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
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Color vision is useful…
http://www.neitzvision.com/content/home.html
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Color vision in Old World Primates (including humans) is trichromatic
Jacobs and Nathans, Scientific American, April 2009
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Red and green genes are very similar and are likely due to a duplication event (unequal crossover) and gene co-option
Jacobs and Nathans, Scientific American, April 2009
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Both males and females are trichromatic…
Jacobs and Nathans, Scientific American, April 2009