24 Human Population Genetics

Question 1

What are the differences between human and chimp DNA?

Answer 1

Differ at 1% of nucleotides
30 million differences in total
9 differences per gene

Question 2

When did modern humans emerge in Africa?

Answer 2

200-300 Kya

Question 3

What is the multiregional model?

Answer 3

Transition from H.erectus to H.sapiens took place in many places - gene flow between populations
- Pop size must have been large
- Humans should show high genetic diversity
- TMRCA 1-2mya

Question 4

What is the Out of Africa model?

Answer 4

TMRCA Less than 200 Kya H.sapiens emerged in Africa then spread around the globe, replacing other hominids
- Small pop size
- Humans should have low genetic diversity
- African pops should have greatest diversity

Question 5

How diverse are humans in relation to other apes?

Answer 5

Humans are the least diverse
- Compatible with Out of Africa model

Question 6

How can we estimate the TMRCA of all humans?

Answer 6

By comparing genetic distance between humans, with the human-chimp distance

Question 7

What types of DNA are useful for determining evolutionary relationships?

Answer 7

Mitochondrial DNA
- Maternally inherited only so doesn’t recombine
- Many copies per cell

Y chromosome DNA
- Paternally inherited only
- Do not recombine with X chromosome

Question 8

What evidence is there that humans and other hominids have interbred?

Answer 8

1) Two ancient lineages of head louse
- Diverged before human existence
- One lineage worldwide, one only in new world
- One had human host, other had different hominid host

2) Between 1 and 4 % of the Eurasian human genome seems to come from Neanderthals (were not in Africa)

Question 9

How have humans adapted to new environments when moving out of Africa?

Answer 9

Skin colour
Diet - e.g. lactase persistence
Disease - heterozygote resistance

Question 10

When did modern humans leave Africa?

Answer 10

Within the last 80kya

Question 11

Why is melanin important?

Answer 11

Bare skin is at risk from UV radiation damage - sunburn, cancers, nutrient photodegradation

In Africa dark skin necessary for protection against UV
- Means little vit D produced
- Strong selection to retain dark pigment

In Europe light skin necessary for vit D production

Question 12

Why is lactase persistence an adaptation?

Answer 12

Milk important for:
Lactose, additional water, calcium

Lactase persistence inherited as an autosomal dominant Mendelian trait