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Recovering the Brownian Coalescent Point Process from the Kingman Coalescent by Conditional Sampling

Abstract : We consider a continuous population whose dynamics is described by the standard stationary Fleming-Viot process, so that the genealogy of $n$ uniformly sampled individuals is distributed as the Kingman $n$-coalescent. In this note, we study some genealogical properties of this population when the sample is conditioned to fall entirely into a subpopulation with most recent common ancestor (MRCA) shorter than $\varepsilon$. First, using the comb representation of the total genealogy (Lambert & Uribe Bravo 2016), we show that the genealogy of the descendance of the MRCA of the sample on the timescale $\varepsilon$ converges as $\varepsilon\to 0$. The limit is the so-called Brownian coalescent point process (CPP) stopped at an independent Gamma random variable with parameter $n$, which can be seen as the genealogy at a large time of the total population of a rescaled critical birth-death process, biased by the $n$-th power of its size. Secondly, we show that in this limit the coalescence times of the $n$ sampled individuals are i.i.d. uniform random variables in $(0,1)$. These results provide a coupling between two standard models for the genealogy of a random exchangeable population: the Kingman coalescent and the Brownian CPP.
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https://hal.archives-ouvertes.fr/hal-01394651
Contributor : Amaury Lambert <>
Submitted on : Wednesday, November 9, 2016 - 3:16:37 PM
Last modification on : Thursday, April 2, 2020 - 1:28:50 PM

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  • HAL Id : hal-01394651, version 1
  • ARXIV : 1611.01323

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Amaury Lambert, Emmanuel Schertzer. Recovering the Brownian Coalescent Point Process from the Kingman Coalescent by Conditional Sampling. 2016. ⟨hal-01394651⟩

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