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Archiver > GENEALOGY-DNA > 2004-09 > 1094451271


From: "gordon hutton" <>
Subject: Re: [DNA] Jobling et al on Recombination
Date: Mon, 6 Sep 2004 07:14:39 +0100
References: <090520042134.5690.413B8651000F26040000163A2200748184050B989A0E00@comcast.net>


A few years ago I was breeding Thoroughbred Horses for Racing .After reading
everything Icould get my hands on. The Italian man (he bred good race horses
out of poor stock by close inbreeding Line breeding they called it) one
thing which stuck in my mind was that Colts were geneticaly 55% to 45%
closer to there mothers. and that
colts with the mothers colouring were unlikely to follow the sire in is
abilities.
Gordon
----- Original Message -----
From: <>
To: <>
Sent: Sunday, September 05, 2004 10:34 PM
Subject: Re: [DNA] Jobling et al on Recombination


> Yes, and one other factor to consider is that males are more likely to
have a larger generic input from their mothers than their fathers.
>
> The X chromosome of a male comes from his mother. The Y from the father
is relatively inert, with a small portion at the tips capable of
recombination. Thus if one were to add up genes, after taking into
condideration recombination of the autosomes, we are left with a functional
equation where a son has his mother's X chromosome to exert its effect,
however his sister's genomic structure has an X from the mother and father -
thus effectively diluting the genetic input of the mother. This is of
course cause for alarm in some cases since, for example in a family with
Duchesne Muscular Dystrophy, half of the male children will have the
mother's X with the defective protein manufacturing capability, and the
females, even in the worse case scenario, will simply be like their mothers,
carriers - but not manifest the disorder clinically since the father's X can
manufacture the protein needed to keep the muscles intact.
>
> Bottom line, sons are more like their mothers genetically, even though
sons carry the almost intact Y chromosome of their father. Interesting,
n'est pas.
>
> David.
>
>
> --
> Dr. David K. Faux
> P.O. Box 192
> Seal Beach, CA 90630
>
>
> www.davidkfaux.org
>
>
> -------------- Original message --------------
>
> > 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: itâ?Ts 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.
> >
> > â?oThe 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 â?~desertâ?T and â?~jungleâ?T 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.�
>
>
> ==============================
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