Race Flashcards
1
Q
Significance of genetic variation?
A
- 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)
2
Q
Is there such thing as race?
A
- Immense genetic variation from individual to individual
- 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 - A very small number of genetic traits vary together (races are social categories)
- Differences are breaking down as migration and intergroup mating is more widespread than ever
3
Q
Cause of genetic variation
A
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
4
Q
Genetic Drift
A
- Non-adaptive
- 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
5
Q
Gene Flow
A
- Non-adaptive
- Exchange of genes between populations e.g. migration, restriction in mate choice
- Genetic clines (gradients) may be evidence of human migration history
6
Q
Founder Effect (Y Chromosomes in Asia)
A
- 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
7
Q
Were the Vikings resistant to HIV-1?
A
- 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
8
Q
Tracing historical diasporas
A
- 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
9
Q
Genetic evidence of African Jews
A
- 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
10
Q
Adaptive Factors: Examples of Natural Selection Causing Genetic Diversity
A
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
11
Q
Melanin
A
- An adaption through natural selection to exposure to sunlight
- Or sexual selection for lighter females in areas of high latitudes?