Lecture 8: Human Genetic Variation Flashcards
What are the four models or the origins of modern humans?
Candelabra, multiregional, replacement, assimilation
What is the candelabra model?
Modern humans evolved independently from other ancestral hominid species in Africa, Asia and Europe
What is the multiregional model?
There was gene flow between the regions so any important genetic changes would have spread quickly.
What is the replacement model?
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
What is the assimilation model?
A combination of the evidence for African origin of modern humans.
What did Luca Cavalli-Sforza do and find out?
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.
What is a haplotype?
A set of SNPs that are inherited together
What did a mtDNA study reveal?
A more recent common ancester - mt Eve was 200,000 ya.
What model did the mt Eve study support?
The out of Africa model
What is different about the continents other than Africa and what does this imply?
They all have multiple origins implying they were colonised repeatedly.
How can restriction enzyme mapping give a profile of each individual?
By analysing the size of the fragments cut by restriction enzymes and mutations will affect the size of these fragments
What methods all support the out of Africa model?
Nuclear, mt and Y chromosome methods
Which continent has the highest diversity?
Africa
What do none-African populations have?
A subset of the variations present in African populations
Why are mitochondria used?
Passed from mother to daughter without recombining. Contain their own genome. Sequenced more easily than nuclear genomes. Been used to map migration since 80s.
How do we think migration to Australia was achieved?
Facilitated by migration along the south coast of Asia
What is surprising about the migration from North to South America?
Took less than 1000y as were walking along the coastal route
What is the Y chromosome?
Largest segment of non-recombining DNA in the human genome
What can we use to estimate when modern humans first evolved?
mt or Y chrs
What is more likely if you sample more people?
Finding the true coalescence time to a single ancestor
What happens to the other ancestors?
By chance, natural selection, stochastic variations, all ancestors end up with no descendents
What will different genes show?
Different patterns of evolution as they will coalesce at different times
Who was mt Eve?
She lived 130-200,000 ya and is the single female ancestor
All men can trace their ancester back to when?
120,000 ya single man.
What gives more recent estimates of coalescence, mt or Y chromosome ? Why?
Y chr. Higher levels of sexual selection among males so fewer males than female contributed to the next generation.
What should the coalescence times of monogamous species be and why?
Males and females should equally contribute to next gen so coalescence times similar.
What is the coalescence time for polygamous species?
Smaller proportion of males expected to contribute to next generation so males have more recent common ancestor
What are coalescence times highly dependent on?
Sampling
Did europeans ever interbreed with neanderthals?
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.
What does Y and mtDNA evidence reveal?
No evidence of interbreeding
What did initial genome analysis show?
Genomes from other humans are more similar to Europeans compared to Europeans and Neanderthals
About how much archaic DNA is there in Europeans?
About 5%
What evidence is there to support some interbreeding?
European ancestry people have on average 3% Neanderthal DNA. Hybrids may have been sterile or interbreeding was rare
Where is there higher levels of neanderthal ancestry?
Eastern Asians than Europeans
Where is there an enrichment of Neanderthal haplotypes?
In or around genes involved in the production of keratin filaments so they may have made some contribution to hair/skin phenotypes.
What is the evidence against Neanderthal DNA?
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.
