= Identical-by-descent segment
= IBD segment
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An identical-by-descent segment is a chromosomal tract inherited from the same ancestral chromosome without an intervening breakpoint in the tracked ancestry. With a specified total number $m$ of independent <meioses> and a uniform recombination map, the probability that a fixed tract of genetic length $d$ survives without <genetic recombination> is approximately $e^{-md}$. Recent common ancestry therefore tends to give longer shared tracts. Lengths of tracts selected by covering a random point are length-biased relative to tracts sampled by their boundaries.
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