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Archiver > GENEALOGY-DNA > 2002-04 > 1018626906


From: (Ellen Keyne Seebacher)
Subject: Re: [DNA] Testing Australian parents' DNA + 'other' genetic material
Date: Fri, 12 Apr 2002 11:55:10 -0400 (EDT)
In-Reply-To: <015501c1e1f2$e3b1cc60$5319fe3f@robert>


Bob Green asks:

> My question now: you make the point that, "The male has his mother's
> DNA but he doesn't pass it on."

No. Males have their mother's *mtDNA*, but do not pass it on. mtDNA
is a small molecule existing only in the mitochondria, outside the
nucleus of the cell; nuclear DNA is a different kettle of fish. The
reason mtDNA passes through the maternal line is that your mitochondria
come from the cytoplasm in your mother's egg.

> I understand this, but wonder if there is other genetic material
> from his mother that he does pass on to children. The same for the
> female side: It seems to me there 'must' be some genetic connection
> between me and my mother's father, even if my mother, lacking the
> Ycs, could not pass that on to me.

Of course. You (assuming you're male) have 46 chromosomes, only one
of which is a Y. Your X (again, assuming you're male) came from your
mother, who could have gotten it from her mother _or_ her father.

The other 44 (22 pairs, sometimes called "autosomes") come from both
your parents in equal measure. So approximately 22 chromosomes' worth
of genes came from your mother, 11 of those from your mother's father
(and so on, dividing by two each generation you go back). You just
have no way of knowing _which genes_, because genes on autosomes
recombine -- they exchange genetic material between members of a pair.

Recombination is why we focus on the types of DNA which are passed
down unchanged and can clearly identify a line of descent: Y sex
chromosomes, in the nucleus, from grandfather to father to son
(remember that X chromosomes, unlike Y, can be passed through male
and female lines); mtDNA, in the mitochondria, from grandmother to
mother to daughter.

I hope this helps clarify things for you!

--
Ellen Keyne Seebacher

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