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I’ll
try to explain DNA testing as I understand it. First for genealogy there
are primarily three types of testing. Y-DNA, MTDNA, X & Autosomal
chromosome testing.
Now to
explain the testing, you have to understand DNA. Each cell of the body
has 23 pairs of chromosomes, in the cell but not in the nucleus
is mtdna. Notice here, the 23 pairs of chromosomes do
not include mtdna.
When, the egg is fertilized the egg has 23 chromosomes and the
sperm has 23 chromosomes. One pair of the chromosomes is used to
indicate the sex of a child. The egg always carries a X chromosome and
the rest are autosomal chromosomes. The sperm carries either the Y or
the X chromosome and the rest are autosomal chromosomes.
Now if it is a boy child, you have a X and a Y for the pair of
sex chromosomes.. Being there is only one “Y”… it cannot combine
or recombine with every generation.
So the Y chromosome basically stays the same with few mutations
(changes) over generations.
So a man’s parental (father/son) lineage can be proven by the results
of the markers used in the Y-STR test.
I should
add here that there are about 3 billion, 300 million Plus spots
(markers/bases) that can be tested. There are different markers used for
different tests. The markers used for Y-DNA testing normally are called
Short Tandem Repeats (STRs)
and single-nucleotide
polymorphism (SNPs
– pronounced Snips). SNPs normally are used for population migration.
Where STRs are used for current genetic genealogy (basically - or in our
case).
single-nucleotide
polymorphism:
http://en.wikipedia.org/wiki/Single-nucleotide_polymorphism
short
tandem repeat:
http://en.wikipedia.org/wiki/Short_tandem_repeat
My
Gilpin surname DNA project:
http://freepages.family.rootsweb.com/~bonsteinandgilpin/
Y-chromosome
DNA testing
FROM
23and me
The Y chromosome is only present in males, and in one copy.
Because the Y, unlike the X and autosomes, undergoes no *recombination* (or at least very little), it travels through the generations as a block,
and therefore all of its SNPs record the same path through human history. This fact permits the ancestry of the Y to be resolved in much
finer geographic detail than the recombining chromosomes.
~~~~~~~~~~~
The
first to understand is that to find a
DNA match the haplogroup of the pair of results being compared must
match.. Example a man who has R1b haplogroup is not related
(with in the time frame of the use of surnames – 1000 – 2000
yrs) to a man who has a Ib1
haplogroup.
Hapolgroups,
depending on the testing company can be estimated by the first 12 STR
markers of a Y-STR marker test. (normally test names are
just referred to by the number of markers tested as in 12
–25-36-44-67) To actually prove a haplogroup or to find a subclade of a
haplogroup; a haplogroup test normally referred to as a deep clade test
should be preformed. Also some companies test for particular haplogroup
SNP markers. The markers tested for haplogroups are called SNPs.
Haplogroups,
are the identifying terminology, for where you sit on the tree of
humanity, it starts off with haplogroup Adam.. and after changes
(mutations) in his SNPs a new haplogroup is created.. so over a few tens
of thousands years, there
developed many different
haplogroups. Some are descend and some are lateral
developments. That is
why a man who has R1b and a man who has I1b are thousands of years apart
from a common ancestor.
Questions?
Ask me.. (oh, Y haplogroups are named differently from mtdna haplogroups)
Now
getting down to the very easiest, the Y-STR test used for genealogy. I
said before that they are basically referred to (or called/named) by the
numbers. The 37 marker, YSTR
test is the one I ask the members of my surname projects to use.
It has enough Fast mutating and slow mutating STR markers to make
it a good identifying amount, the more markers the better but normally 37
is enough. What they do here is introduce a primer to the dna base at a
particular place and count the reactions (spikes). The amount of reactions
at a particular place (marker/base) is the result (there is an official
name but it is still just a result)
To
prove or disprove a relationship you compare the amount of the result to
the result of the other person. So example: man A - marker
DYS393=12; man B – DYS393=14 the
steps of difference here is 2, all differences are accumulative.
At 37 markers, in my opinion; more then 4-5 steps of difference
between two men make the common ancestor
before the use of surnames.. Thus in the realm of current
genealogy.. not related.
See:
Y-DNA
results:
http://www.worldfamilies.net/surnames/gilpin/results?raw=1
MTDNA
Testing
the
ratio size of sperm to egg is exaggerated here so you can see the
MTDNA in both.
Next
is MTDNA – mtdna is a chromosome but not part of the 23 pairs. It has a
different job, it is primarily to produce and direct energy for the cell.
Its mutations are very slow. A test of the MTDNA can have medical
information. If you know what MTDNA SNP mutations indicate what medical
information.
MTDNA
is in both the cell of the egg and the sperm. But the mtdna of the sperm
is primarily there to give energy to the sperm to swim to the egg and
impregnate it. Normally all
the mtdna in the sperm is used up, when it isn’t the egg destroys the
remainder. Thus you inherit the mtdna in your cells from only your mother.
That is the reason it can be used to trace the maternal lineage. MTDNA, is
different from the other chromosomes in that instead of being a string it
is circular, and it is normally tested in HRV1 and HRV2 and the coding
zone. I was told HRV1 and 2 start basically
if you were looking at a clock -
at 11:59 and end at 12:06 the rest is coding zone..and there are about
17,000 SNPs to test.
It
is hard to use MTDNA for genealogy because
the maiden name changes with each generation where a man’s surname is
passed to each generation. I
said hard, but it is not impossible, there have been many positive
results. You look for
matching maiden names and
area locations.. Then you put the findings together. A matched maiden
name, a matched time frame, a matched location, and matching mutations.
When
testing MTDNA the results are very different from what you get with Y-DNA
testing. There is a standard called Cambridge
Reference Sequence, your results are compared to this and only the
differences (mutations) are reported. So in this case you compare
differences. To match, you and the person comparing must be the same
differences from the CRS.
Mtdna
– http://en.wikipedia.org/wiki/Mitochondrial_DNA
http://en.wikipedia.org/wiki/Human_mitochondrial_DNA_haplogroup
X and
autosomal testing
Total 23 pairs
Now
lets discuss the newest testing.. X and autosomal testing.
First,
you inherit these 22 pairs of Autosomal chromosomes and the "X"
chromosome from all your past ancestors (X chromosome inheritance pattern
is a little different then the autosomals), second you might think you
inherit 50% from each parent. NOPE…you inherit the equal to
50%. Since the X chromosome and the autosomal chromosomes
combine and recombine randomly, (x to x; auto to auto) the
further away from the common ancestor the lower the chance you have
a measurable segment remaining from that ancestor. One problem that I see
with this testing is that a negative result of a measurable segment from a
common ancestor does not mean your not related, just that the part
inherited is not measurable at this time.
(You
never know – this is cutting edge science.... five years ago.. this
testing was not possible…the future holds surprises! ).
Now
here is some additional information from some very knowledgeable people..
Nelda
From
- Dr. Ann Turner in an
email to me:
Females
have two X chromosomes, one inherited from the father and the other
from the mother, so a connection in the X chromosome could be from either
side of the family.
Males have one X chromosome, inherited from the mother. SMGF has a nice
animation showing the inheritance pathway:
http://www.smgf.org/education/animations/x_chromosome.jspx
Since not all ancestors can make a contribution to the X, you can
eliminate
at least some of them as possibilities. See the diagrams on Blaine
Bettinger's site:
http://www.thegeneticgenealogist.com/2008/12/21/unlocking-the-genealogical-secrets-of-the-x-
chromosome/
http://www.thegeneticgenealogist.com/2009/01/12/more-x-chromosome-charts/
Note that the percentages are AVERAGES. A man's X chromosome can be
exactly
the same as his maternal grandfather, exactly the same as his maternal
grandmother, or a mixture of the two, which works out to be average of
50%. I
find the demo Mendel family at 23andMe helpful in visualizing this. There
are
three grandchildren and three grandparents, so you can look at different
combinations. (for 23 & me members) If they don't show up in your list
of people you're sharing with, go to Account | Sharing | Example Profiles.
It
will help you to phase the X (in other words, figure out who contributed
what). This page helps tell how to do that:
http://www.isogg.org/xjourney1.html
If your genealogy program can print an ahnentafel chart, I've prepared a
file with the relevant ahnentafel numbers. Females should start the
ahnentafel
with themselves; males should start with their mothers. Then you can go
through the ahnentafel report and delete the records of the people who
could
not be the source of your X.
http://dnacousins.com/AHN_X.TXT
The
Chart
If your a female then you put your name in
the number one place. If your male then your mother goes in the number one
position. blue is male #2 is your father, pink-female #3
is your mother
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