GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2004-09 > 1094418418
From: "Nancy Custer" <>
Subject: Jobling et al on Recombination
Date: Sun, 5 Sep 2004 14:06:58 -0700
Below is pretty much a verbatim copy of a few paragraphs from Jobling, et al about recombination. I omitted a few bits out of laziness that I didn't think added to the question at hand. Bottom line: it’s very complicated and can't be reduced to a few simple numbers.
(If you are wondering what the heck recombination even is, I have a vastly oversimplified animation of meiosis with recombination at http://www.contexo.info/DNA_Basics/Meiosis.htm.)
Jobling, M. A., M. E. Hurles, and C. Tyler-Smith, Human Evolutionary Genetics (New York: Garland Publishing, 2004) pages 37-38.
“The distribution of recombination events varies between the sexes: females have more recombination events when they make eggs than males do when they make sperm: in other words, the genetic map of females is expanded on average about 1.65-fold with respect to that of males (a graph is given on page 38.) Males have roughly 50 recombination events per meiosis, whereas females experience 80 such events. Also, the recombination rate across the genome within each sex is far from uniform. Recombination events are more frequent toward the telomeres of chromosomes and less frequent towards their centromeres. Regional variation is present on many scales: recombination rates are on average about twice as high on the smallest chromosomes compared with the largest, but both recombination ‘desert’ and ‘jungle’ segments can be identified within chromosome arms.
"These average values over large chromosomal regions could obscure substantial recombination rate heterogeneity at the sequence level. Direct molecular analysis of recombination indicates that, for some regions of the genome at least, events are concentrated in small segments of DNA known as recombination hotspots, separated by comparatively large regions of low recombinational activity. There could be as much as 1000-fold difference in recombination rates between hotspots and cold domains. This nonuniformity of recombination takes on great importance when we come to consider the issue of the distribution of sequence variants along chromosomes in different human populations. Furthermore, significant variations in recombination rates in pedigree data can be detected between individual women, although not between individual men.
. . . "Most chromosomes undergo on average just over one recombination event per chromosomal arm, and it seems that these events are necessary for the faithful segregation of chromosomes into daughter cells at division.”