GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2001-02 > 0982505013


From: Richard Gethmann <>
Subject: Re: [DNA] Ancestor identification
Date: Sun, 18 Feb 2001 09:03:33 -0500
References: <3.0.16.20010218072926.1d075372@pop.erols.com>




William Addams Reitwiesner wrote:

> At 08:05 PM 02/17/2001 -0600, you wrote:
>
> <snip>
>
> >Do you think it is possible to eventually not be related to an actual
> ancestor at
> >all, genetically? (Assuming no non-paternal events, just that the DNA from
> that
> >ancestor eventually dilutes out of existence.)
>
> Not only is it possible, it's necessary, and in not all that many generations.
>
> Every human has 46 chromosomes, 23 from each parent. You probably got a
> dozen from each grandparent, less than six from each of your
> great-grandparents, and so on. You have 64 different
> great-great-great-great-grandparents and only 46 chromosomes, so quite a
> few of your ancestors, only seven generations back, contributed *no*
> chromosomes to you.
>

The above would be true if an event called crossing over didn't happen. However,
crossing over happens between all chromosome pairs. Let's use chromosome #1 as
an example. The chromosome #1 you inherited from your mother is most likely a
composite consisting of part of the chromosome #1 she inherited from her mother
and part of the chromosome #1 she inherited from her father. I've tried to
illustrate this below:

A B C D E F
a b c d e f

If each sequence of letters above represents one of the two chromosomes #1 your
mother contains, then what did you receive from her? You will have one that
contains both some upper case letters and lower case letters. For example, you
could have the combination:

A B c d e F

The likelihood of receiving a chromosome from either of your parents that has not
undergone a crossover is quite small.

Thus, it is safe to assume that your genetic makeup represents an equal
contribution from each of your ancestor levels ( i.e. - 1/2 from each of your
parents, 1/4 from each grandparent, 1/8 from each g grandparent and so on).

--
****************************************
RC Gethmann

****************************************
When you have eliminated the impossible,
whatever remains, however improbable,
must be the truth
A. Conan Doyle


This thread: