Lecture 8: Human Genetic Variation

Question 1

What are the four models or the origins of modern humans?

Answer 1

Candelabra, multiregional, replacement, assimilation

Question 2

What is the candelabra model?

Answer 2

Modern humans evolved independently from other ancestral hominid species in Africa, Asia and Europe

Question 3

What is the multiregional model?

Answer 3

There was gene flow between the regions so any important genetic changes would have spread quickly.

Question 4

What is the replacement model?

Answer 4

Transformation to modern humans occurred in a single population in Africa 200,000 to 300,000 ya which spread out of Africa 50-100,000 ya and replaced any archaic humans from earlier migrations

Question 5

What is the assimilation model?

Answer 5

A combination of the evidence for African origin of modern humans.

Question 6

What did Luca Cavalli-Sforza do and find out?

Answer 6

Started studying human migration patterns from church records in Italy. He studies the frequencies of blood types. The B globin gene cluster polymorphisms supported the out of Africa model. The most likely site of origin for a species is the place where you find the most unique African variants.

Question 7

What is a haplotype?

Answer 7

A set of SNPs that are inherited together

Question 8

What did a mtDNA study reveal?

Answer 8

A more recent common ancester - mt Eve was 200,000 ya.

Question 9

What model did the mt Eve study support?

Answer 9

The out of Africa model

Question 10

What is different about the continents other than Africa and what does this imply?

Answer 10

They all have multiple origins implying they were colonised repeatedly.

Question 11

How can restriction enzyme mapping give a profile of each individual?

Answer 11

By analysing the size of the fragments cut by restriction enzymes and mutations will affect the size of these fragments

Question 12

What methods all support the out of Africa model?

Answer 12

Nuclear, mt and Y chromosome methods

Question 13

Which continent has the highest diversity?

Answer 13

Africa

Question 14

What do none-African populations have?

Answer 14

A subset of the variations present in African populations

Question 15

Why are mitochondria used?

Answer 15

Passed from mother to daughter without recombining. Contain their own genome. Sequenced more easily than nuclear genomes. Been used to map migration since 80s.

Question 16

How do we think migration to Australia was achieved?

Answer 16

Facilitated by migration along the south coast of Asia

Question 17

What is surprising about the migration from North to South America?

Answer 17

Took less than 1000y as were walking along the coastal route

Question 18

What is the Y chromosome?

Answer 18

Largest segment of non-recombining DNA in the human genome

Question 19

What can we use to estimate when modern humans first evolved?

Answer 19

mt or Y chrs

Question 20

What is more likely if you sample more people?

Answer 20

Finding the true coalescence time to a single ancestor

Question 21

What happens to the other ancestors?

Answer 21

By chance, natural selection, stochastic variations, all ancestors end up with no descendents

Question 22

What will different genes show?

Answer 22

Different patterns of evolution as they will coalesce at different times

Question 23

Who was mt Eve?

Answer 23

She lived 130-200,000 ya and is the single female ancestor

Question 24

All men can trace their ancester back to when?

Answer 24

120,000 ya single man.

Question 25

What gives more recent estimates of coalescence, mt or Y chromosome ? Why?

Answer 25

Y chr. Higher levels of sexual selection among males so fewer males than female contributed to the next generation.

Question 26

What should the coalescence times of monogamous species be and why?

Answer 26

Males and females should equally contribute to next gen so coalescence times similar.

Question 27

What is the coalescence time for polygamous species?

Answer 27

Smaller proportion of males expected to contribute to next generation so males have more recent common ancestor

Question 28

What are coalescence times highly dependent on?

Answer 28

Sampling

Question 29

Did europeans ever interbreed with neanderthals?

Answer 29

Archaelogical evidence places us with them in the same geographical area and we alternate occupancy lots. One skull has been found that could be a hybrid.

Question 30

What does Y and mtDNA evidence reveal?

Answer 30

No evidence of interbreeding

Question 31

What did initial genome analysis show?

Answer 31

Genomes from other humans are more similar to Europeans compared to Europeans and Neanderthals

Question 32

About how much archaic DNA is there in Europeans?

Answer 32

About 5%

Question 33

What evidence is there to support some interbreeding?

Answer 33

European ancestry people have on average 3% Neanderthal DNA. Hybrids may have been sterile or interbreeding was rare

Question 34

Where is there higher levels of neanderthal ancestry?

Answer 34

Eastern Asians than Europeans

Question 35

Where is there an enrichment of Neanderthal haplotypes?

Answer 35

In or around genes involved in the production of keratin filaments so they may have made some contribution to hair/skin phenotypes.

Question 36

What is the evidence against Neanderthal DNA?

Answer 36

Their DNA is less frequent within genes than we expected. Ther is reduced frequency in testes expressed genes and X chromosomes which can play a role in driving hybrid male sterility.