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Archiver > GENEALOGY-DNA > 2002-12 > 1038844270


From: "J. M. Freed" <>
Subject: [DNA] X and Y chromosome inheritance.
Date: Mon, 2 Dec 2002 10:51:10 -0500
References: <1a6.cd945e8.2b1bb68c@aol.com>


Over the past few months, I've seen several examples of mistakes in
interpretation about the inheritance of the X and the Y chromosomes as
evidenced by the following comment recently made on this list:

"What remains, for over 500 generations, without mutation, is the Y &
X chromosome markers, inherited by males from their father and by
females from their mother."

True, Y chromosomes in males are inherited ONLY from their fathers.
However, all females (exception in Turner Syndrome individuals who
have only one X chromosome) inherit one X chromosome from their father
and one X chromosome from their mother. Also both Y and X
chromosomes markers ARE subject to mutations; without mutations these
chromosomes would be of no value for genealogical studies.

Further, the two X chromosomes in a specific female cannot be stated
as coming from two specific great grandparents, In fact, because of
the process of crossing-over (where actual chromosomal material is
literally exchanged between two like chromosomes), each X chromosome
in a female is highly likely to have origins in multiple great
grandparents, not just two great grandparents.

The above is the explanation of why the "Y chromosome" (inherited only
from the father in males) and the mitochondrial chromosome (inherited
only from the mother in both males and females) are of such tremendous
value for genealogical studies. On the other hand, the X chromosome
is of very little significance for genealogical studies over a long
number of generations.

Jim
Instructor of Genetics

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