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Solving the Fisher-Wright and coalescence problems with a discrete Markov chain analysis

Published online by Cambridge University Press:  01 July 2016

Samuel R. Buss*
Affiliation:
University of California, San Diego
Peter Clote*
Affiliation:
Boston College
*
Postal address: Department of Mathematics, University of California, San Diego, La Jolla, CA 92093, USA. Email address: sbuss@ucsd.edu
∗∗ Postal address: Department of Biology, Boston College, Chestnut Hill, MA 02467, USA. Email address: clote@bc.edu

Abstract

We develop a new, self-contained proof that the expected number of generations required for gene allele fixation or extinction in a population of size n is O(n) under general assumptions. The proof relies on a discrete Markov chain analysis. We further develop an algorithm to compute expected fixation or extinction time to any desired precision. Our proofs establish O(nH(p)) as the expected time for gene allele fixation or extinction for the Fisher-Wright problem, where the gene occurs with initial frequency p and H(p) is the entropy function. Under a weaker hypothesis on the variance, the expected time is O(n(p(1-p))1/2) for fixation or extinction. Thus, the expected-time bound of O(n) for fixation or extinction holds in a wide range of situations. In the multi-allele case, the expected time for allele fixation or extinction in a population of size n with n distinct alleles is shown to be O(n). From this, a new proof is given of a coalescence theorem about the mean time to the most recent common ancestor (MRCA), which applies to a broad range of reproduction models satisfying our mean and weak variation conditions.

Type
General Applied Probability
Copyright
Copyright © Applied Probability Trust 2004 

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Footnotes

Supported in part by NSF Grant DMS-9803515 and DMS-0100589

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