Recent Explosive Human Population Growth Has Resulted in an Excess of Rare Genetic Variants

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Recent Explosive Human Population Growth Has Resulted in an Excess of Rare Genetic Variants

Alon Keinan and Andrew G. Clark

R00922079 王淳毅 R00944039 柯彥圻 R00945042 林培鈞

12年6月3日星期日

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Introduction

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Human population have experienced recent

explosive growth, expanding by at least three orders of magnitude over the past 400 generations.

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Introduction

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Human population have experienced recent

explosive growth, expanding by at least three orders of magnitude over the past 400 generations.

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Introduction(cont’d)

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We characterized the empirical signatures of explosive growth on the site frequency spectrum.

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The discrepancy in rare variant abundance across demographic modeling studies is

mostly due to difference in sample size.

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Earlier studies used small amounts of data and did not observe population growth.

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However, these studies did not capture the full scope of human expansion, which may be due to the models not allowing for a recent acceleration in growth rate.

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There are several differences between the models of population history assumed by the different

studies that considered recent population growth—

as well as between the inference methods used—

that can potentially explain the differences in results (Table 1).

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However, we hypothesize that the very different results are mostly due to

differences in sample size.

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A larger sample size allows identification of rare polymorphisms that are, on average,

due to more recent mutations.

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The excess of rare variants found with a large sample size predicts a growth of 5 to 14% per generation over the past 900 to 2800 years,

compared to models of smaller sample size that predicted growth of between 0.2 and 0.7% over a longer period of 20,000 to 30,000 years.

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The expected site frequency spectrum(SFS) of the derived allele (the new mutation

arisen in the population) for three different demographic models.

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Sample size exceeds the effective size of the population

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Λ-coalescent theory(neutral variation): a

retrospective(look back) model of population genetics

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^θ=4N^еμ >>1, the vast majority of allele pairs have at least one difference in nucleotide sequence

Ne

: eﬀec%ve popula%on

μ: per-‐site muta%on rate

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The fraction of novel variants discovered in each sequenced genome decreases in all

models as more individuals are sequenced.

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Recombina%on will not have broken down linkage disequilirium between rare

muta%on and neighboring common variants.

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It is imperative to understand the impact of nature selection during the phase of

explosive growth.

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Thanks for your attention!