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Can genes help explain our evolution?- What type of changes (regulatory
or structural mutations?)
- How many genes are involved?
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Approaches to Identify Genetic/Genomic Differences Between Chimps and Humans
1. Candidate gene approach
2. Microarray approach
3. Nucleotide substitution approach
4. Bioinformatic approach
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Enard, W. et al. 2002. Molecular evolution of FOXP2, agene involved in speech and language. Nature 418, 869-872.
Candidate gene approach: FOXP2
- 2 non-conservative amino acid substitutions in humans-- flanking genomic DNA showed signs of a selective sweep
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Signature of a Selective Sweep
Reduced polymorphismMore rare alleles
FavoredAllele
SelectionFixation
RecombinationMutation
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• FOXP2 is expressed highly in zebra finches during the vocal learning period of development.Haesler et al. 2004. J. Neurosci 24:3164.
• FOXP2 knock-out mice have altered motorsensoryfunctions and ultrasonic vocalizations.Shu et al. 2005. PNAS 102:9643.
FOXP2 plays a role in the development of brain regions that are important for communication
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Pollard, KS et al. An RNA gene expressed during corticaldevelopment evolved rapidly in humans. Nature Aug. 2006
• Scanned the 2/3 portion of the genome that is non-coding
• Many of the identified regions are associated with transcription factors and neurodevelopment genes.
• The most dramatically changed element (HAR1) is a novel RNA gene expressed during human cortical development.
Identified Human Accelerated Regions (HARs)
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- Search chimpanzee genome sequence against rat and mouse genome sequences. (96% identity > 100 bp)
- 35,000 regions identified
- Searched these regions in all other available amniote genomes searching for regions with significant changes in human.
- 49 regions identified with a statistically significant rate increase in humans (96% in non-coding regions, 24% next to a neurodevelopmental gene)
Details of the Screening Process