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The region of chromosome 2 (234,876,004–234,884,481 bp; NCBI build 34) within ENr131.2q37 contains 36 SNPs, with zero obligate recombinaNon events in the CEU samples.
A haplotype map of the human genome HapMap Nature 2005
“The discovery of [..] Coalescent is arguably one of the most important theoreNcal discoveries in all of biology over the past 50 years.” Nielsen 2016 GeneNcs
T2(=2 gens) T3 (=14 gens) T4 (=2gens)
Generations
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The coalescent for sample sizes greater than two T M
RCA(=18 gens)
Generations
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T2 (=9 gens) T3 (=4 gens) T4 (=2gens)
The coalescent for sample sizes greater than two
T MRC
A(=15 gens)
From Nordborg 2000
The coalescent for sample sizes greater than two
You don’t increase the informaNon about the tree much from increasing your sample size
From Nordborg review
There is liale informaNon about underlying processes in a single genealogy
Generations
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T2 (=9 gens) T3 (=4 gens) T2 (=2gens)
The coalescent for sample sizes greater than two
CCTG
A
CGTG
A
TCTG
A CGTC
A TCTGA
CGTCA
CGTGA
CGTGA Given the total length of the tree L, the expected number of segregaNng sites is Lμ
The frequency of an allele in the sample reflects the branch in the genealogy on which the branch occurred.
CCTGA
CGTGA
CGTGT
TCTGA
TCTGA
TCTGA
CCTCA
CGTGA
CGTGA
CGTGT
1 2 3
# copies
CCTCA
Frequency spectrum for derived neutral alleles
Expectations for the unfolded site-frequency spectra
Sample size Theoretical spectrum (singletons, doubletons, ...)2 �3 �, �/24 �, �/2, �/35 �, �/2, �/3, �/4
General solution: Expected count of sites at frequency i is equal to�i .
Curious property: As sample size increase, number of singletons,doubletons, etc. stays the same, just a new category is added.TCTGA
TCTGA
TCTGA
CCTCA
CCTCA
A balance between mutaNon, drie and SelecNon could explain our frequency spectrum for NS sites
T
A growing population
No
NT
Slower coal. rate towards the tips, compared with a stationary population.
What does the genealogy look like in a recently expanded populaNon?
Excess of singletons
T
A bottlenecked population
N
neutral No
faster coal. here
What does the genealogy look like if there was a recent boaleneck?
Can lead to excess of intermediate freq.alleles Leading to high variance
T
N
Locus 1 2 3 4 5
T
N
EffecNve populaNon size (x104)
Gene
raNo
ns back
Generations
Past Present
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●Barriers to migraNon amongst populaNons Allow independent drie and differenNaNon Lower rates of migraNon &/or smaller populaNon sizes (higher rates of drie)
Drie creates allelic differenNaNon between populaNons if migraNon
rates are low & divergence Nmes are long
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