Race

Question 1

Significance of genetic variation?

Answer 1

• 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)

Question 2

Is there such thing as race?

Answer 2

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

Question 3

Cause of genetic variation

Answer 3

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

Question 4

Genetic Drift

Answer 4

• 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

Question 5

Gene Flow

Answer 5

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

Question 6

Founder Effect (Y Chromosomes in Asia)

Answer 6

• 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

Question 7

Were the Vikings resistant to HIV-1?

Answer 7

• 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

Question 8

Tracing historical diasporas

Answer 8

• 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

Question 9

Genetic evidence of African Jews

Answer 9

• 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

Question 10

Adaptive Factors: Examples of Natural Selection Causing Genetic Diversity

Answer 10

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

Question 11

Melanin

Answer 11

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