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Human Migrations Saeed Hassanpour Spring 2008
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Introduction Population Genetics Co-evolution of genes with language and cultural. Human evolution: genetics, history, statistics, physical/social anthropology, archaeology, demography, linguistic,...
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Background Genetic variation discovery: ABO blood groups (1919). Biochemical methods(e.g. PCR): stain, radioactive, fluorescent markers visualization. DNA sequencing and genotyping
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Definition Allele: Different forms of a gene. Genotype: The specific allele in an individual. Phenotype: The expression of a genotype. Allele Genotype Phenotype Homozygote Heterozygote
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Definition Microsatellite: Short consecutive repeats: Single nucleotide polymorphism (SNP): Variation in a single nucleotide of a genome between two individuals. AC
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Definition Linkage disequilibrium (LD): Correlation between alleles at two different position. Haplotype: Combination of alleles at multiple linked loci which are transmitted together.
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Evolution Evolutionary forces: Natural selection: Probability of survival and reproduction Genetic drift: Change in allele frequencies entirely by chance.
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Evolution Mutation: Change in nucleotide sequence of genes caused by copying error or exposure to radiation, chemical substance, viruses,... Migration
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Genetic Distance Fixation Index (F st ): Measure of population differentiation. Π Between (Π Within ): Average number of pairwise difference between two individuals sampled from different (the same) population. Π Between Π Within
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Natural selection Find Genes which are candidates to have been under selection: Very low and very high F st distance. Compare expected and observed values of F st.
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Evolutionary History F st matrix analysis: Phylogenetic tree Based on SNP of 120 genes in 1,915 individuals
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Evolutionary History Principle components Based on 783 microsatellite s in 1,027 individuals
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Mitochondrial DNA Mitochondrial DNA (mtDNA): In mitochondria (out of nucleus) transmitted along only female lineages. No recombination. High mutation rate: Abundance of polymorphic Difficult genealogy reconstruction
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NYR and Autosome None-recombining part of Y chromosome. Lower rate of the mutation Greater length of DNA Autosome: non-sex chromosome.
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TMRCA Time of the fist major separation in evolutionary tree between african and non- african. Bayesian analysis and maximum-likelihood methods: Using mtDNA: TMRCA≈230,000 Using NRY: TMRCA≈100,000
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TMRCA Polygyny vs. Polyandry
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F st Matrix Analysis Oceania America E.Asia C.S.Asia Europe Midl.East Africa Based on 650,000 SNPs in 938 individuals
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F st Matrix Analysis F st vs. geographic distance Based on SNP of 120 genes in 1,915 individuals
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F st Matrix Analysis (A) Europe, (B) The Middle East Based on 650,000 SNPs in 938 individuals
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Genetic variance Partition molecular variance in Autosome, ChrX, Microsatellite: Within population(WP) Among-population -within-group(AP/WG) Among geographical region(AG)
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Migration
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Waypoints Based on 783 microsatellite s in 1,027 individuals
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Heterozygosity α: population in Africa. p ~ ui: probability of allele u in population i Estimate of heterozygosity in population i:
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Heterozygosity Expansion of modern human from a single center. Each migration is a sampling from the original population. (Serial Founder) K NbNb K K 12n NbNb
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Heterozygosity Considering only genetic drift No migration between populations n bottleneck, N b founders at each bottleneck Reduction in heterozygosity by factor: 1-1/(2N b )
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Heterozygosity
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HumanChimp ?
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Drift vs. Selection Since regression explain 76%-78% of observed genetics variation Lower bound on genetic drift effect: 76%-78% Upper bound on Selection effect: 22%-24%
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Genes and Culture Culture transmission: Vertically and Horizontally
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Conclusion Out of Africa theory explain the Human genetic diversity: Genetic distance Heterozygosity
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Refrences The application of molecular genetic approaches to the study of human evolution, Cavalli-Sforza & Feldman, 2003 Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa, Ramachandran et al., 2005 Worldwide Human Relationships Inferred from Genome from Genome-Wide Patterns of Variation, Jun Li et all., 2008
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