I'm forwarding this from another list because it is an interesting question.
Lee Anne
----- Original Message -----
From: "Dale Marr" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, November 03, 2003 9:54 PM
Subject: [ARIZARD-L] Genetic Testing
> > I have a dumb question I hope you will take the time to answer. If a
> distant ancestor were only like 1/16 Indian, would that reduce by each
> generation until there were no markers, or are the original genetic
> markers there forever?
>
> My first thought was that this thread should be labeled "off topic," but
if you think about it genetics is the very foundation of genealogy. It's
not a dumb question at all. It sounds like a logical conclusion at first
glance, but the different types of markers (in the case of American Indian
testing, mtDNA and Y-chromosome) don't get "reduced" in each generation.
I'm certainly no authority, but this is the way I understand it.
>
> Y-marker testing is done for the markers on the Y chromosome (and
obviously only on males). This chart shows four generations of males. As
you can see each male child gets all the information on his Y chromosome
from his father who got all the information from his father and so on....
It doesn't get "diluted" from one generation to the next just like the ABO
blood types don't dilute. (Determining blood types of your ancestors is
kind of interesting, too.) Humans have 22 other pairs of chromosomes with
all kinds of information that does get diluted.
>
> XX=female, XY=male
>
> 1 XY + XX
> . | |
> . -------
> . |
> 2 XY + XX
> . | |
> . -------
> . |
> 3 XY + XX
> . | |
> . -------
> . |
> 4 XY
>
> MtDNA testing is done on a male or female at the end of a female-to-female
line. Mitochondrial DNA (mtDNA) is a different kind of DNA from that in the
nuclei of cells. It's in the mitochondria, those little thingies that
supply energy to the cell. You have the same "set" of mtDNA as your mother,
your maternal grandmother, your maternal grandmother's mother, and so on....
>
> This chart shows four generations of females. Though a female gets an X
chromosome from each parent, and a male gets an X chromosome from his mother
and a Y chromosome from his father, each gets ALL his or her mtDNA from the
mother. The male doesn't pass along any mtDNA, represented by the lower
case "m", to his children. Rather his children get all their mtDNA from
their mother who got it from her mother, etc. If you follow the upper case
"M" in each generation and think of that as a "package" containing the mtDNA
(oversimplified but illustrates the point), you can see it doesn't get
diluted as it's passed to each generation.
>
> 1 MXX + mXY
> . | |
> . -------
> . |
> 2 MXX + mXY
> . | |
> . -------
> . |
> 3 MXX + mXY
> . | |
> . -------
> . |
> 4 MXX
>
> This is another site that has a lot of information and a much better chart
than I can draw here. http://www.familytreedna.com/tcnam.html Of my two
charts above, the first one corresponds to the blue line and the second one
corresponds to the red line in their complete chart.
>
> Dale
>
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