4: Human pop. genetics

Question 1

Describe human and chimpanzees relationship

Answer 1

Humans and chimpanzees diverged ~5-7 mill yrs ago, we differ about 1% of nucleotides
- So on average ~9 differences per gene humans compared to chimps

Question 2

Describe the Australopithecines

Answer 2

Important group: hominids that arose ~4.2 MYA (looked more like humans than chimps) → thought to be ancestors of genus Homo

Australopithecus afarensis ~3.0-3.9 MYA
Most famous fossil of this species called “lucy”, footprints found nearby suggest they were bipedal

Question 3

Describe Homo erectus

Answer 3

~2.5 MYA. found in all continents, we think they arose in Africa first
Earliest hominid outside Africa ~1.6-1.9 MYA in Java

Question 4

Describe Homo heidelbergensis

Answer 4

~ 1 MYA
Descended from H. erectus in Africa

Question 5

Describe Homo neanderthalensis

Answer 5

~ 28.250 KYA
Descended from Homo heidelbergensis

Question 6

What are the 2 theories about when and where modern humans arose?

Answer 6

Multiregional model VS Out-of-Africa

Question 7

Describe the multiregional model

Answer 7

Humans evolved independently from H.erectus on diff continents.
- Gene flow between pop.s so high genetic diversity
- No prediction that diversity should be greather on certain continents
- TMRCA should be ~1-2 MYA

Question 8

Define the Out-of-Africa model

Answer 8

Asian and European pop.s extinct, and H. sapiens evolved only in Africa 200KYA and then spread to the rest of the world (replacing other hominids e.g H. erectus)
- pop. size small so low genetic diversity
- African pop.s should have highest gen diversity
- TMRCA < 200 kya

Question 9

Describe whether genetic diversity differs between human pop.s

Which model does this support?

Answer 9

• Data shows the more distant the pop. is from East Africa, the less genetic diversity they have
• Also, for most genetic markers, African pop.s are more diverse

= Supports the Out-Of-Africa model

Question 10

describe how and why we would calibrate a molecular clock?

Answer 10

• To look at the most recent common ancestor
• We can measure genetic distance between chimps and humans and we know they diverged 5-7 MYA

= By comparing the genetic distance between humans with the human-chimp distance we can estimate the TMRCA of all humans

Question 11

The first attempts at TMRCAs used which non-recombining molcules?

Answer 11

Mitochondrial DNA
Y chromosome DNA

Question 12

Could humans and other hominids have interbred?

Answer 12

Head louse study:
- ancient lineages of louse diverged, one worldwide other only New World, one human host, other diff hominid
= Suggest humans and hominids weren’t interbreeding for a long time

Neanderthal DNA study:
- sequences analysed, neanderthals distinct from modern humans
= no interbreeding

Question 13

Give some examples of adaptive genetic variance in humans

Answer 13

• Adaptive melanism to changes in climate
• Adaption to diet (lactase)
• Adaption to disease (CF)

Question 14

Describe the role of melanin in humans

Answer 14

Most important skin pigment in relation to colour
Eumelanin synthesis → associated with black/brown pigments
Phaeomelanin synthesis → associated with red/yellow pigments

Question 15

What caused such a strong selection for dark skin?

Answer 15

The negative effects of UV radiation:
- Long term exposure can cause skin/eye cancers
- Nutrient photodegradation e.g Flavins, carotenoids and folate degraded
- Folate deficiency can cause neural tube defects (e.g spina bifida)

Dark skin helps protect from UV

Question 16

Why is light skin, adaptivley necessary in Europe?

Answer 16

Light skin necessary for vit D production, especially as high grain diet is vit D poor
UV levels are lower

Question 17

Describe how lactase persistence is an adaptation

Answer 17

• In most pop.s the ability to digest lactose decreases after weaning (lactose intolerance)
  Lactase persistance (most prevalent in Northern Europe and Central Africa), why?
• Lactose (food), additional water (important inn arid regions), calcium
• Lactase persistence inherited as an autosomal dominant Mendelian trait
• Persistence allele (LCTP) is dominant to lactose intolerance allele (LCTR)