Genes in populations 3 Flashcards
roughly when did hominids and other great apes diverge?
5.7 million years ago
what are the 2 arguments for where humans arose?
multi regional vs out of Africa
what is the multi regional theory?
a single population spread over many continents connected by gene flow with high genetic diversity and transitioned from H. erectus to H. sapiens
what is the out of Africa theory?
humans originated out of a limited area of Africa with a low genetic diversity H. sapiens replaced H.erectus
2 pieces of evidence to support out of Africa model
1) compared to our closest relatives humans are not very diverse
2) all alleles share a common ancestor
5 features of mitochondrial DNA
1) found in both sexes
2) maternally inherited only
3) small molecules
4) high mutation rate
5) many copies per cell
3 features of Y chromosome DNA
1) found in males only
2) paternally inherited only
3) do not recombine with X chromosome
when did humans emerge in Africa and when did they spread?
the emerged 120-140 thousand years ago and they spread 30-80 thousand years ago
what is evidence go show that skin colour is adaptive?
dark skin in Africa to protect from UV - little Vitamin D produced so more needed in diet
light skin in Europe due to high grain diet with low vitamin D and low UV levels
what is the gene best studied for pigmentation?
MCR1
how is lactase persistent inherited?
autosomal dominant mendelian trait - persistance allele is dominant to lactose intolerance allele
what are heterozygotes to cystic fibrosis resistant to?
cholera and typhoid
why is there a higher frequency of cystic fibrosis heterozygotes in Europe?
because they are resistant to infectious diseases which are more common in agricultural societies
when did agriculture and domestication take place?
within the last 10 thousand years
what is cladogenesis?
the formation of a new group of organisms by evolutionary divergence (speciation)
what is post zygotic isolation?
a new gene causing sterility or inviability of hybrids and will not spread through a population
what is pre zygotic isolation?
a new gene causing an altered mating signal or response also likely to spread through a population
what is disruptive selection and how does it cause speciation?
intense competition at high abundance therefore low fitness and weak competition at 2 areas of low competition therefore high fitness of 2 groups forming two species
what is assortative mating?
2 distinct groups only breed with themselves
what is allopatric speciation?
separation by an ecological barrier
what is the founder effect?
where genetic drift can overcome the section of sterile hybrids but only in very small populations
what is the Dobzhansky- Muller solution?
traits A and B are both fixated and advantageous to each population but the hybrids of both genes joined together are not advantageous and incompatible
what is autopolyploidy?
multiple chromosome sets derived from the same species that produce unstable pairing
what is allopolyploidy?
polyploids with chromosome sets derived from different species to produce stable pairing
where is polyploidy common?
in plants
what may polyploidy result in?
instant speciation
what is isolation of a species due to?
incompatibilities between separately evolved traits/genes
