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Flashcards in Race Deck (11)
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Significance of genetic variation?

-Much is insignificant biologically
-neutral mutations alter the amino acid sequence of the resulting protein but produce no detectable change in it's function
-silent mutations do not even change the amino acid sequence
-changes to non-coding, non-regulatory DNA sequences (this used to be called junk DNA)


Is there such thing as race?

1.Immense genetic variation from individual to individual
2.BUT there is almost as much variation within any local group as there is across the whole world (Lewontins 85%)
-Diversity was lost when humans suffered severe bottlenecks e.g. leaving Africa or entering the Americas
3.A very small number of genetic traits vary together (races are social categories)
4. Differences are breaking down as migration and intergroup mating is more widespread than ever


Cause of genetic variation

non-adaptive factors
-gene flow e.g. migration history
-genetic drift e.g. founder effects
adaptive factors
-natural selection
-sexual selection
Geneticists disagree as to whether adaptive or neutral factors is the greatest cause of genetic diversity


Genetic Drift

-Random factor in evolution tied to population size
-if drift is the major cause of genetic change, the degree of divergence between populations is related to
-time separation
-population size


Gene Flow

-Exchange of genes between populations e.g. migration, restriction in mate choice
-Genetic clines (gradients) may be evidence of human migration history


Founder Effect (Y Chromosomes in Asia)

-Age (1000 years), place of origin (Mongolia) and modern distribution of Y Chromosomes haplotype (xC3c 8% of Asian Y Chromosomes)
-Suggests Y Chromosomal lineage of Genghis Khan and his immediate ancestors (c1162-1227) who established a long lasting male dynasty
-Now carried 0.5% of world's men


Were the Vikings resistant to HIV-1?

-Delta-32 mutation
-Homozygous carriers of the gene are resistant to HIV1
-Predates emergence of HIV1
-Could be explained by:
-Gene Flow- viking mediated disperal
- Selection - small pox or plague as the selective agent


Tracing historical diasporas

-Identification of particular mtDNA or Y chromosomal haplotype at high frequency can sometimes be taken as a population measure
-Y chromosomes of mtDNA are useful because they don't recombine
-Y, X and mtDNA are useful because they are sex linked
-However, lack of interbreeding makes migration/gene flow easier to detect


Genetic evidence of African Jews

-Lemba (S.W. Africa) have a Y chromosome known as the 'Cohen model haplotype' traceable to the Jewish Priesthood
-Ethiopian Jews (the beta israel) have Y chromosomes haplotypes indistinguishable from those of other Ethiopians


Adaptive Factors: Examples of Natural Selection Causing Genetic Diversity

Lactose digestion capacity
-evolving with pastoralism
Skin colour
-evolving with sunshine
Haemoglobinopathies (e.g. HbS)
-evolving with malaria
-All these genes show different patterns of geographical diversity, because the agents that select for them have different geographic ranges



-An adaption through natural selection to exposure to sunlight
-Or sexual selection for lighter females in areas of high latitudes?