DNA - Can you enlighten?

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Leo van de Pas

DNA - Can you enlighten?

Legg inn av Leo van de Pas » 16 jan 2006 23:46:02

Dear Todd,

Like many, DNA is a very mysterious world to me. The discussion at the moment is very interesting. There is one aspect I wonder about, but more wonder whether I am wrong.

A person gets 50% of DNA from his/her father and 50% from his/her mother.

Now that 50% from the father, where did that come from? Does he pass on half of _his_ father and half of _his_ mother? So that the grandchild would have 25% from each grandparent?

I read somewhere that a person could have an ancestor, many generations ago, and not have any DNA from that ancestor, is that correct?

I think, I am not the only one wondering about this.
Look forward to hearing from you.
Leo van de Pas

Denis Beauregard

Re: DNA - Can you enlighten?

Legg inn av Denis Beauregard » 17 jan 2006 00:03:02

Le Mon, 16 Jan 2006 21:59:41 +0000 (UTC), leovdpas@netspeed.com.au
("Leo van de Pas") écrivait dans soc.genealogy.medieval:

Dear Todd,

Like many, DNA is a very mysterious world to me. The discussion at the moment is very interesting. There is one aspect I wonder about, but more wonder whether I am wrong.

A person gets 50% of DNA from his/her father and 50% from his/her mother.

Now that 50% from the father, where did that come from? Does he pass on half of _his_ father and half of _his_ mother? So that the grandchild would have 25% from each grandparent?

You have 23 pairs of chromosoms. 22 are the same for men and women.
During the processus of creation, each 22 chromosoms of the man are
connected to those of the woman, and results are 22 new chromosoms
containing each some genes from the father and some from the mother.

So, it is possible you get 80% of genes from the father and 20% from
the mother.

As for the sexual chromosoms, XX for the women and XY for the men:
the XX are mixed so that a part of the new X chromosom is from both
the father and the mother. The Y and the other X are transmitted as
is I think.

The overall result is that any gene is from either the father or the
mother. Weaker genes can less likely survive to the next generation,
i.e. it seems the genepool is improving at the next generation. But
the Y is the same, so it keeps its weakness. I remember an article
when someone claimed that in a long run, that Y was weaker with the
generations while the X (and the 22 other pairs) were regenerating
so that the humankind may disappear in some millions of years because
of that.


I read somewhere that a person could have an ancestor, many generations ago, and not have any DNA from that ancestor, is that correct?

If I remind it correctly, there are about 300,000 human genes. If we
don't take into account the XY, I think for any of them, odds are
50:50 to have it from the father or the mother. So, odds a 1:2 power
(300,000) that you have no gene from either the father or mother.

I think, I am not the only one wondering about this.
Look forward to hearing from you.
Leo van de Pas


Denis

--
0 Denis Beauregard -
/\/ Les Français d'Amérique - http://www.francogene.com/genealogie-quebec/
|\ French in North America before 1716 - http://www.francogene.com/quebec-genealogy/
/ | Mes associations de généalogie: http://www.SGCF.com/ (soc. gén. can.-fr.)
oo oo http://www.genealogie.org/club/sglj/index2.html (soc. de gén. de La Jemmerais)

Todd A. Farmerie

Re: DNA - Can you enlighten?

Legg inn av Todd A. Farmerie » 17 jan 2006 02:05:24

Leo van de Pas wrote:

A person gets 50% of DNA from his/her father and 50% from his/her mother.


With the exception of the X and Y chromosomes and mtDNA, yes.


Now that 50% from the father, where did that come from? Does he pass on half of _his_ father and half of _his_ mother? So that the grandchild would have 25% from each grandparent?


Each chromosome pair remixes with each generation, so _statistically_
25% comes from each grandparent, compared to _exactly_ 50% (one of the
pair of chromosomes) coming from each parent.


I read somewhere that a person could have an ancestor, many generations ago, and not have any DNA from that ancestor, is that correct?


Absolutely. With each generation the amount from each ancestor is
divided by (statistically) 1/2. You have about 3,000,000,000 base pairs
in your DNA. Even were it to be exactly 50% and the DNA could actually
be subdivided with single-nucleotide resolution (both of these
assumptions are invalid, but for the sake of argument . . . ), by 32
generations you would have 4,000,000,000 ancestors, and some could not
possibly be represented. In fact, the point is reached much earlier,
because it is not exactly 50%, but statistically 50% and some lineage
will have drawn the short straw, and further, some regions of the DNA
are more prone to recombination than others, so you do not really have
nucleotide-level resolution in this redivision process. (Keep in mind,
too, that most [greater than 99.9%] of this DNA is identical among all
humans, so who it came from is rather immaterial.)

With the mtDNA, all of it comes from the maternal line. (There are a
few documented cases of paternal inheritance, but these are extremely
rare, and there has been no observed mixing of maternal and paternal -
just all or nothing). The Y is (virtually) entirely male-line derived
(an extremely small portion, usually ignored in such discussions, mixes
with a similar portion of the X, just like discussed above).

As to the X, a male gets his entirely from his mother, a female gets one
from each. This means that of a womans Xs, one is a statistical 50/50
mix from her maternal grandparents, while the other is 100% from her
paternal grandmother (the paternal grandfather passed his Y to the
father, and no X comes from him [except for the small portion that can
remix with the Y]). Thus the patralineal line, as well as any line with
two successive males, contribute nothing to the X. Other lines
contribute an amount reduced by 50% (statistically) for each maternal
generation (not reduced for each paternal generation), such that the
matralineal line, the lowest of those represented is simply 1/2
multiplied by itself for the number of generations involved, while the
highest represented lineage is one that alternates
male-female-male-female, and the X contribution is 1/2 times itself for
half the number of generations. THus:

For most DNA, where z - the percent contribution and n - the number of
generations, it is:

z=(1/2)^n * 100%

For the X, where m - the number of female generations:

z=(1/2)^m * 100% OR z=0 when two or more successive males occur

For the matrilineal line, m=n:

z=(1/2)^n * 100%

for the alternating line, m=n/2:

z=(1/2)^n/2 * 100%


(you asked . . . .)

taf

Todd A. Farmerie

Re: DNA - Can you enlighten?

Legg inn av Todd A. Farmerie » 17 jan 2006 02:20:36

Denis Beauregard wrote:
Le Mon, 16 Jan 2006 21:59:41 +0000 (UTC), leovdpas@netspeed.com.au
("Leo van de Pas") écrivait dans soc.genealogy.medieval:

The overall result is that any gene is from either the father or the
mother. Weaker genes can less likely survive to the next generation,
i.e. it seems the genepool is improving at the next generation. But
the Y is the same, so it keeps its weakness. I remember an article
when someone claimed that in a long run, that Y was weaker with the
generations while the X (and the 22 other pairs) were regenerating
so that the humankind may disappear in some millions of years because
of that.

Before everyone goes out and celebrates in the face of our imminant
demise, this is not likely at all. Actually, genes on the Y have slowly
been transferred to the other 22 chromosomes, and it is thought that
either the Y will eventually completely disappear, and gender will then
be determined by one X (male) vs. two (female), or else the Y remnant
will become joined to one of the other 22, which will then become the
'sex' chromosome, and the process will begin again. We are talking,
though, not millions but hundreds of millions of years, with all mammals
in the same boat.

If I remind it correctly, there are about 300,000 human genes.

Too high by a factor of 10 - latest estimates put the number (much to
everyone's surprise) in the high 20,000s. However, the gene is not the
unit of recombination, although we don't know what, exactly, this unit
is. It is smaller than a kilobase (1000 bp unit), and as I pointed out
to Leo, since most humans differ by less than 1 change per kilobase it
is impossible to resolve smaller than this. All that can be said is
that you would have somewhere between 3,000,000 and 3,000,000,000
possible sites of recombination, so you would have to go between 22 and
32 generations (given perfect 50/50 division, which we know does not
happen) to know you have reached the point of an ancestor making no
genetic contribution.

taf

Kelly Gray

Re: DNA - Can you enlighten?

Legg inn av Kelly Gray » 17 jan 2006 02:22:02

thanks todd!

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Kelly Gray

Re: DNA - Can you enlighten?

Legg inn av Kelly Gray » 17 jan 2006 02:42:01

Todd- what about Denis' statement that one could possibly then have DNA from
one's father and mother at the ratio of 80/20?

trying to keep up tonight

thamks
Kelly

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Terry

Re: DNA - Can you enlighten?

Legg inn av Terry » 17 jan 2006 03:42:02

Ok this raises a question for me, in my fathers side of the family we
connect to the Lindsay family, in the last 4 generations three ways, and on
my mothers side more remotely several times, so statistically would I have
more Lindsay DNA then Mair or not?, if that makes sense.
Thanks
Terry L. Mair
Mair's Photography
158 South 580 East
Midway, Utah 84049
435-654-3607
http://www.mairsphotography.com
----- Original Message -----
From: "Todd A. Farmerie" <farmerie@interfold.com>
To: <GEN-MEDIEVAL-L@rootsweb.com>
Sent: Monday, January 16, 2006 6:05 PM
Subject: Re: DNA - Can you enlighten?


Leo van de Pas wrote:

A person gets 50% of DNA from his/her father and 50% from his/her mother.


With the exception of the X and Y chromosomes and mtDNA, yes.


Now that 50% from the father, where did that come from? Does he pass on
half of _his_ father and half of _his_ mother? So that the grandchild
would have 25% from each grandparent?


Each chromosome pair remixes with each generation, so _statistically_ 25%
comes from each grandparent, compared to _exactly_ 50% (one of the pair of
chromosomes) coming from each parent.


I read somewhere that a person could have an ancestor, many generations
ago, and not have any DNA from that ancestor, is that correct?


Absolutely. With each generation the amount from each ancestor is divided
by (statistically) 1/2. You have about 3,000,000,000 base pairs in your
DNA. Even were it to be exactly 50% and the DNA could actually be
subdivided with single-nucleotide resolution (both of these assumptions
are invalid, but for the sake of argument . . . ), by 32 generations you
would have 4,000,000,000 ancestors, and some could not possibly be
represented. In fact, the point is reached much earlier, because it is
not exactly 50%, but statistically 50% and some lineage will have drawn
the short straw, and further, some regions of the DNA are more prone to
recombination than others, so you do not really have nucleotide-level
resolution in this redivision process. (Keep in mind, too, that most
[greater than 99.9%] of this DNA is identical among all humans, so who it
came from is rather immaterial.)

With the mtDNA, all of it comes from the maternal line. (There are a few
documented cases of paternal inheritance, but these are extremely rare,
and there has been no observed mixing of maternal and paternal - just all
or nothing). The Y is (virtually) entirely male-line derived (an
extremely small portion, usually ignored in such discussions, mixes with a
similar portion of the X, just like discussed above).

As to the X, a male gets his entirely from his mother, a female gets one
from each. This means that of a womans Xs, one is a statistical 50/50 mix
from her maternal grandparents, while the other is 100% from her paternal
grandmother (the paternal grandfather passed his Y to the father, and no X
comes from him [except for the small portion that can remix with the Y]).
Thus the patralineal line, as well as any line with two successive males,
contribute nothing to the X. Other lines contribute an amount reduced by
50% (statistically) for each maternal generation (not reduced for each
paternal generation), such that the matralineal line, the lowest of those
represented is simply 1/2 multiplied by itself for the number of
generations involved, while the highest represented lineage is one that
alternates male-female-male-female, and the X contribution is 1/2 times
itself for half the number of generations. THus:

For most DNA, where z - the percent contribution and n - the number of
generations, it is:

z=(1/2)^n * 100%

For the X, where m - the number of female generations:

z=(1/2)^m * 100% OR z=0 when two or more successive males occur

For the matrilineal line, m=n:

z=(1/2)^n * 100%

for the alternating line, m=n/2:

z=(1/2)^n/2 * 100%


(you asked . . . .)

taf


Todd A. Farmerie

Re: DNA - Can you enlighten?

Legg inn av Todd A. Farmerie » 17 jan 2006 04:34:31

Kelly Gray wrote:

Todd- what about Denis' statement that one could possibly then have DNA
from one's father and mother at the ratio of 80/20?

Possible, but unlikely. It would take two things happening together.
Normally you get crossing over between each of the 22 chromosome pairs,
such that each resulting chromosome is partly maternal, partly paternal
(averaging about two crossovers per chromosome pair), and then the cell
division process selects one of the two to go to each progeny gamete
(reproductive cell). In order to get a severe skew, you would have to
both have a skewed recombination within chromosome pairs, such that the
resulting chromosomes show a significant divergence from 50/50
maternal/paternal, and you would have to randomly happen to select each
of the chromosomes that mostly came from a single parent, like flipping
a coin and getting heads, say, 20 out of 22 times (even if each
individual chromosome was mostly maternal or mostly paternal, you would
normally still expect to select roughly half of each).

I don't know the actual experimental results, but I would suspect that
anything beyond 60% would be unusual, and 80% extremely rare.

taf

Todd A. Farmerie

Re: DNA - Can you enlighten?

Legg inn av Todd A. Farmerie » 17 jan 2006 04:50:33

Terry wrote:
Ok this raises a question for me, in my fathers side of the family we
connect to the Lindsay family, in the last 4 generations three ways, and
on my mothers side more remotely several times, so statistically would I
have more Lindsay DNA then Mair or not?, if that makes sense.

Umm. It really doesn't work this way. Other than, perhaps, the Y
chromosome, there is no such thing as "Lindsay DNA" or "Mair DNA" - it
is remixed and exchanged each generation.

If you have three lines of descent from a single person x generations
back, then you are more likely to have that person's DNA (and likely to
have more of that person's DNA) than of anyone else in his generation
(except the male and female line ancestors if you are far enough back).

However, depending on how distantly related they are, three Lindsays may
share little DNA in common among all three of them (the amount shared
being reduced by 1/2 each generation in each line, so if they were third
cousins - 5 generations in each of their three lines, that would be
1/2^15, or 1/32,000). The important point is that this is what would be
'shared' DNA derived from their most recent Lindsay ancestor, but that
is an arbitrary point at which to label the DNA as 'Lindsay DNA': half
of it came from that common ancestor's non-Lindsay mother.

taf

Terry

Re: DNA - Can you enlighten?

Legg inn av Terry » 17 jan 2006 07:11:01

So then how is it that lets say my ancestors came from Scotland and where
Gaels, how can DNA show this if most of the marriages where say Saxons?
Terry L. Mair
Mair's Photography
158 South 580 East
Midway, Utah 84049
435-654-3607
http://www.mairsphotography.com
----- Original Message -----
From: "Todd A. Farmerie" <farmerie@interfold.com>
To: <GEN-MEDIEVAL-L@rootsweb.com>
Sent: Monday, January 16, 2006 8:50 PM
Subject: Re: DNA - Can you enlighten?


Terry wrote:
Ok this raises a question for me, in my fathers side of the family we
connect to the Lindsay family, in the last 4 generations three ways, and
on my mothers side more remotely several times, so statistically would I
have more Lindsay DNA then Mair or not?, if that makes sense.

Umm. It really doesn't work this way. Other than, perhaps, the Y
chromosome, there is no such thing as "Lindsay DNA" or "Mair DNA" - it is
remixed and exchanged each generation.

If you have three lines of descent from a single person x generations
back, then you are more likely to have that person's DNA (and likely to
have more of that person's DNA) than of anyone else in his generation
(except the male and female line ancestors if you are far enough back).

However, depending on how distantly related they are, three Lindsays may
share little DNA in common among all three of them (the amount shared
being reduced by 1/2 each generation in each line, so if they were third
cousins - 5 generations in each of their three lines, that would be
1/2^15, or 1/32,000). The important point is that this is what would be
'shared' DNA derived from their most recent Lindsay ancestor, but that is
an arbitrary point at which to label the DNA as 'Lindsay DNA': half of it
came from that common ancestor's non-Lindsay mother.

taf


Todd A. Farmerie

Re: DNA - Can you enlighten?

Legg inn av Todd A. Farmerie » 17 jan 2006 08:03:38

Terry wrote:
So then how is it that lets say my ancestors came from Scotland and
where Gaels, how can DNA show this if most of the marriages where say
Saxons?

If most of the marriages were Saxons (I assume you mean most of the
wives), then it would be inaccurate to say that your ancestors were
Gaels, unless you are talking about a single specific line. If that is
your male line, then the undiluted Y would be distinctive. If it is any
other line, the distinctive 'Gael" DNA (if there is any such thing),
would be diluted with the Saxon, and probably unrecognizable unless
there is a specific polymorphism unique to the Gaels, and it just
happened to pass down the line.

taf

Terry

Re: DNA - Can you enlighten?

Legg inn av Terry » 17 jan 2006 16:25:02

Just trying to wade through this DNA thing, so lets say there is a direct
ancestor of say Somerled, lets say he goes to England early in history and
lived with the Saxons and married into them, so would DNA prove his decent
from Somerled or maybe not, assuming we had DNA from Somerled? Also even if
his DNA would not prove decent from SOmerled would it show an origin of what
ever group of people Somerled truly was descended from?
Thanks again
Terry L. Mair
Mair's Photography
158 South 580 East
Midway, Utah 84049
435-654-3607
http://www.mairsphotography.com
----- Original Message -----
From: "Todd A. Farmerie" <farmerie@interfold.com>
To: <GEN-MEDIEVAL-L@rootsweb.com>
Sent: Tuesday, January 17, 2006 12:03 AM
Subject: Re: DNA - Can you enlighten?


Terry wrote:
So then how is it that lets say my ancestors came from Scotland and where
Gaels, how can DNA show this if most of the marriages where say Saxons?

If most of the marriages were Saxons (I assume you mean most of the
wives), then it would be inaccurate to say that your ancestors were Gaels,
unless you are talking about a single specific line. If that is your male
line, then the undiluted Y would be distinctive. If it is any other line,
the distinctive 'Gael" DNA (if there is any such thing), would be diluted
with the Saxon, and probably unrecognizable unless there is a specific
polymorphism unique to the Gaels, and it just happened to pass down the
line.

taf


Todd A. Farmerie

Re: DNA - Can you enlighten?

Legg inn av Todd A. Farmerie » 17 jan 2006 17:43:10

Terry wrote:
Just trying to wade through this DNA thing, so lets say there is a
direct ancestor of say Somerled, lets say he goes to England early in
history and lived with the Saxons and married into them, so would DNA
prove his decent from Somerled or maybe not, assuming we had DNA from
Somerled? Also even if his DNA would not prove decent from SOmerled
would it show an origin of what ever group of people Somerled truly was
descended from?

If the descent was in the male line, the Y chromosome would pass
virtually unchanged down the line, ans would still mark the descendant
as a member of the same male kindred to which Somerled belonged (which
could be known from other documented male-line descents). If not in the
male line, then DNA analysis would be virtually useless in determining
such relationships, unless something extremely unusual happened.

taf

Doug McDonald

Re: DNA - Can you enlighten?

Legg inn av Doug McDonald » 17 jan 2006 18:23:54

Todd A. Farmerie wrote:

Before everyone goes out and celebrates in the face of our imminant
demise, this is not likely at all. Actually, genes on the Y have slowly
been transferred to the other 22 chromosomes, and it is thought that
either the Y will eventually completely disappear, and gender will then
be determined by one X (male) vs. two (female), or else the Y remnant
will become joined to one of the other 22, which will then become the
'sex' chromosome, and the process will begin again. We are talking,
though, not millions but hundreds of millions of years, with all mammals
in the same boat.

This is in fact not now thought to be true. The Y chromosome has
at least one mechanism that keeps it working properly, and others
are suspected. And of course, sex chromosomes have been around
a very very long time, and have kept working fine all that time.
Birds, for example, have a similar system to mammals, just
reversed (females have the special chromosome, males have
two copies of the non-special one.)

Doug McDonald

Doug McDonald

Re: DNA - Can you enlighten?

Legg inn av Doug McDonald » 17 jan 2006 19:10:03

Todd A. Farmerie wrote:
Terry wrote:
So then how is it that lets say my ancestors came from Scotland and
where Gaels, how can DNA show this if most of the marriages where say
Saxons?

If most of the marriages were Saxons (I assume you mean most of the
wives), then it would be inaccurate to say that your ancestors were
Gaels, unless you are talking about a single specific line. If that is
your male line, then the undiluted Y would be distinctive.

Perhaps. The Y-haplogroup R1b reaches almost 100% in the most
"Gaelic" parts of Ireland. But it also dominates in Germany and
Spain. There are R1b haploTYPES that are probably "mostly"
Gaelic, with emphasis on the "mostly".

If it is any
other line, the distinctive 'Gael" DNA (if there is any such thing),
would be diluted with the Saxon, and probably unrecognizable unless
there is a specific polymorphism unique to the Gaels, and it just
happened to pass down the line.


Currently no unique "Gaelic" markers are known.

That said, it is more likely that eventually AUTOSOMAL
characteristics will be found that can with reasonable
probability say "Gaelic", just as ones are already known
that say "African" or European" or "from India".

Doug McDonald

Doug McDonald

Re: DNA - Can you enlighten?

Legg inn av Doug McDonald » 17 jan 2006 19:23:44

Terry wrote:
Just trying to wade through this DNA thing, so lets say there is a
direct ancestor of say Somerled, lets say he goes to England early in
history and lived with the Saxons and married into them, so would DNA
prove his decent from Somerled or maybe not, assuming we had DNA from
Somerled? Also even if his DNA would not prove decent from SOmerled
would it show an origin of what ever group of people Somerled truly was
descended from?


DNA alone cannot "prove" descent from Somerled, since we do not
know of any mutation that he and he alone carried on his Y chromosome.
There is a 50% chance the WAS one, we just don;t know what it was.
What we do know was the signature of his descendant "Good John",
from the DNA of people with paper trails to three of his sons.

What "matching" DNA actually says is that somebody, such as me,
is a male line descendant of Good John or a close cousin. It is
actually quite likely that we will eventually find, through DNA
tests and paper trails, a mutation that does indeed uniquely distinguish
descendants of one of the men in the line from Somerled to
Good John or at least isolate a distinctive mutation to a stretch
of men three or so generations long. This is because this line
is having the most attention of any male line in the world given to it.
It has all the characteristics which make it a likely candidate
for success.

Doug McDonald

Terry

Re: DNA - Can you enlighten?

Legg inn av Terry » 17 jan 2006 22:13:01

Thanks,
Terry L. Mair
Mair's Photography
158 South 580 East
Midway, Utah 84049
435-654-3607
http://www.mairsphotography.com
----- Original Message -----
From: "Todd A. Farmerie" <farmerie@interfold.com>
To: <GEN-MEDIEVAL-L@rootsweb.com>
Sent: Tuesday, January 17, 2006 9:43 AM
Subject: Re: DNA - Can you enlighten?


Terry wrote:
Just trying to wade through this DNA thing, so lets say there is a
direct ancestor of say Somerled, lets say he goes to England early in
history and lived with the Saxons and married into them, so would DNA
prove his decent from Somerled or maybe not, assuming we had DNA from
Somerled? Also even if his DNA would not prove decent from SOmerled
would it show an origin of what ever group of people Somerled truly was
descended from?

If the descent was in the male line, the Y chromosome would pass
virtually unchanged down the line, ans would still mark the descendant
as a member of the same male kindred to which Somerled belonged (which
could be known from other documented male-line descents). If not in the
male line, then DNA analysis would be virtually useless in determining
such relationships, unless something extremely unusual happened.

taf


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