Archiver > GENEALOGY-DNA > 2010-02 > 1265884847

From: "Andrew Mceachern" <>
Subject: Re: [DNA] Puzzled
Date: Thu, 11 Feb 2010 05:40:47 -0500

May I suggest (perhaps to be ridiculed) that in the big picture it is to ensure we have genetic diversity in the human species.

-----Original Message-----
From: "Andrew Mceachern" []
Date: 11/02/2010 08:11 PM
Subject: Re: [DNA] Puzzled

Here's a historical study based on those phenomenal Icelandic genealogies:

Am J Hum Genet. 2003 Jun;72(6):1370-88. Epub 2003 Apr 29.

A populationwide coalescent analysis of Icelandic matrilineal and
patrilineal genealogies: evidence for a faster evolutionary rate of mtDNA lineages
than Y chromosomes.

Helgason A, Hrafnkelsson B, Gulcher JR, Ward R, Stefánsson K.

deCODE Genetics, Reykjavík, Iceland.

Historical inferences from genetic data increasingly depend on assumptions
about the genealogical process that shapes the frequencies of alleles over
time. Yet little is known about the structure of human genealogies over long
periods of time and how they depart from expectations of standard
demographic models, such as that attributed to Wright and Fisher. To obtain such
information and to examine the recent evolutionary history of mtDNA and
Y-chromosome haplotypes in the Icelandic gene pool, we traced the matrilineal and
patrilineal ancestry of all 131,060 Icelanders born after 1972 back to two
cohorts of ancestors, one born between 1848 and 1892 and the other between 1798
and 1742. This populationwide coalescent analysis of Icelandic genealogies
revealed highly positively skewed distributions of descendants to ancestors,
with the vast majority of potential ancestors contributing one or no
descendants and a minority of ancestors contributing large numbers of descendants.
The expansion and loss of matrilines and patrilines has caused considerable
fluctuation in the frequencies of mtDNA and Y-chromosome haplotypes, despite
a rapid population expansion in Iceland during the past 300 years. Contrary
to a widespread assumption, the rate of evolution caused by this
lineage-sorting process was markedly faster in matrilines (mtDNA) than in patrilines
(Y chromosomes). The primary cause is a 10% shorter matrilineal generation
interval. Variance in the number of offspring produced within each generation
was not an important differentiating factor. We observed an
intergenerational correlation in offspring number and in the length of generation intervals
in the matrilineal and patrilineal genealogies, which was stronger in
matrilines and thus contributes to their faster evolutionary rate. These findings
may have implications for coalescent date estimates based on mtDNA and Y

PMCID: PMC1180299
PMID: 12721957 [PubMed - indexed for MEDLINE]

In a message dated 2/10/2010 10:36:07 PM Pacific Standard Time,

> Why do lineages daughter out?
> How many do? Over what period of time?

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