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Human Migrations

Human Migrations

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Human Migrations

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  1. Human Migrations Saeed Hassanpour Spring 2008

  2. Introduction Population Genetics Co-evolution of genes with language and cultural. Human evolution: genetics, history, statistics, physical/social anthropology, archaeology, demography, linguistic,...

  3. Background Genetic variation discovery: ABO blood groups (1919). Biochemical methods(e.g. PCR): stain, radioactive, fluorescent markers visualization. DNA sequencing and genotyping

  4. Definition Allele: Different forms of a gene. Genotype: The specific allele in an individual. Phenotype: The expression of a genotype. Allele Homozygote Phenotype Heterozygote Genotype Homozygote

  5. Definition Microsatellite: Short consecutive repeats: Single nucleotide polymorphism (SNP): Variation in a single nucleotide of a genome between two individuals. AC AC AC AC AC AC AC AC

  6. Definition Linkage disequilibrium (LD): Correlation between alleles at two different position. Haplotype: Combination of alleles at multiple linked loci which are transmitted together.

  7. Evolution Evolutionary forces: Natural selection: Probability of survival and reproduction Genetic drift: Change in allele frequencies entirely by chance.

  8. Evolution Mutation: Change in nucleotide sequence of genes caused by copying error or exposure to radiation, chemical substance, viruses,... Migration

  9. Genetic Distance Fixation Index (Fst): Measure of population differentiation. ΠBetween(ΠWithin): Average number of pairwise difference between two individuals sampled from different (the same) population. ΠBetween ΠWithin

  10. Natural selection Find Genes which are candidates to have been under selection: Very low and very high Fst distance. Compare expected and observed values of Fst.

  11. Evolutionary History Fst matrix analysis: Phylogenetic tree Based on SNP of 120 genes in 1,915 individuals

  12. Evolutionary History Principle components Based on 783 microsatellites in 1,027 individuals

  13. 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

  14. NYR and Autosome None-recombining part of Y chromosome. Lower rate of the mutation Greater length of DNA Autosome: non-sex chromosome.

  15. 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

  16. TMRCA Polygyny vs. Polyandry

  17. Fst Matrix Analysis Oceania America E.Asia C.S.Asia Based on 650,000 SNPs in 938 individuals Europe Midl.East Africa

  18. Fst Matrix Analysis Fst vs. geographic distance Based on SNP of 120 genes in 1,915 individuals

  19. Fst Matrix Analysis (A) Europe, (B) The Middle East Based on 650,000 SNPs in 938 individuals

  20. Genetic variance Partition molecular variance in Autosome, ChrX, Microsatellite: Within population(WP)‏ Among-population -within-group(AP/WG)‏ Among geographical region(AG)‏

  21. Migration

  22. Waypoints Based on 783 microsatellites in 1,027 individuals

  23. Heterozygosity α: population in Africa. p~ui: probability of allele u in population i Estimate of heterozygosity in population i:

  24. Heterozygosity Expansion of modern human from a single center. Each migration is a sampling from the original population. (Serial Founder)‏ K K K Nb Nb 1 2 n

  25. Heterozygosity Considering only genetic drift No migration between populations n bottleneck, Nb founders at each bottleneck Reduction in heterozygosity by factor: 1-1/(2Nb)

  26. Heterozygosity

  27. Heterozygosity

  28. Heterozygosity ? Human Chimp

  29. 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%

  30. Genes and Culture Culture transmission: Vertically and Horizontally

  31. Conclusion Out of Africa theory explain the Human genetic diversity: Genetic distance Heterozygosity

  32. 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