Human population genetics

Question 1

When (and where) humans emerged as a species

Answer 1

Humans and chimps diverged 〜 5-7 MYA (closest living relative)

Homo erectus 〜 2.5 MYA in Africa

Homo sapiens 〜 250-300 KYA in Morocco

Question 2

When humans colonised the world

Answer 2

Multiregional model
-Transition from H.erectus to H.sapiens took place in many areas
-Gene flow between populations

Out-of-Africa model
-Less than 200KYA
-H.sapiens emerged in africa then spread around the globe, replacing other hominids e.g. H.erectus

Out-of-Africa model is correct
-Compared to nearest relatives (other apes), we are not very diverse
-The african population is more genetically diverse
-TMRCA is a few hundreds of thousands of years
-Therefore data suggests that humans spread out of Africa 〜 30-80KYA

TMRCA = time to most recent common ancestor

H.sapiens interbred with other hominids (neanderthals)

Question 3

How humans have adapted to climate

Answer 3

Skin colour
-Melanin pigment affects skin colour
—–Eumelanin synthesis = black/brown pigments
—–Phaeomelanin synthesis = red/yellow pigments
-Negative effects of UV
—–Short term exposure - sunburn, sweat gland damage
—–Long term exposure - skin/eye cancer
-Positive effects of UV
—–Synthesis of vitamin D, if without - rickets

In Africa
-Dark skin necessary for UV protection
-Little vitamin D produced, so have a high vitamin D diet

In europe
-Light skin necessary for vitamin D production
-UV levels lower

Under strong selection in africans, dark pigment retained

Question 4

How humans have adapted to diet

Answer 4

Lactase is an enzyme that digests lactose (milk sugar)

Usually, lactase levels diminish post-weaning

In some populations, lactase persistence lasts into adulthood

Most frequent in populations with history of pastoralism

Lactase persistence allele is dominant to lactose intolerance allele