Hi,
I have created a FREE website to help people understand DNA
testing better and I thought I would share it with all of you.
As a DNA project administrator for some surname projects at
FamilyTreeDNA.com I like to share information about testing. If any of you who
have tested share any of my project surnames, your welcome to join my groups as
well. You can do this via the join button on your personal page at FTDNA.
Now to explain the testing, you have to have a little understanding of DNA. Each cell of the body has 23 pairs of chromosomes, in the
cell nucleus. 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.
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| Here sperm is larger then normal |
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).
single-nucleotide polymorphism:
short
tandem repeat:
There are three basic tests for genetic genealogy
1. the testing of Y-DNA, this test uses the STR marker and defines the direct paternal line.
To define: it is your father his father his father back a few hundred thousand years or more.
More information below.
2. MTDNA this test uses the SNP markers and is used to define the direct maternal line.
To define: this is the child, the mother, her mother, her mother back a few hundred thousand years or more.
More information below.
Only your differences from the Cainbridge Standard are reported for this test. Although,
there are different levels to testing the MTDNA you do not get the entire picture with out the Full test.
More information below.
3. atDNA tests the autosomal chromosomes, it uses the SNP markers. Every person has autosomal
chromosomes to include the individuals who provided the Y chromosome and the mtDNA,
so atdna comes from both the Maternal lineage and the Paternal lineages – Everyone in your ancestry.
The test shows segments on the different chrosomes , that you share with others indicating a relationship.
With this test the terms IBD and IBS are used. IBD means identical by descent and IBS identical by state.
atDNA consists of the 22 autosomal chromosome pairs, these are part of the 23 pairs of nucleus
chromosomes. The 23rd pair is the sex indicator pair and consists of the XX for females and
the YX for males.
MTDNA In human beings, the mitochondrial DNA is a single, small, circular chromosome.
It is not part of the 23 pairs of nucleus chromosomes. Many of them live inside the cell but not in the
enclosed nucleus. They have a different job. MTDNA directs the creation and use of energy in each
individual cell.
Where nucleus chromosomes have 3billion, 300million plus a few hundred thousand base pairs;
MTDNA only has about 16,569 base pairs
 |
| The cell nucleus |
The X chromosome is tested by some companies at the same
time as the atDNA. It uses the SNP marker and althought is part of the sex
indicator pair
does not define the maternal
line. The X passes back and forth between a man and a woman, its line of
descent is different and needs a chart to help you understand who you got it
from. Like the “Y” and “MTDNA”, it has a particular path. See the X chart here:
http://geneticsand.us/x-ch.htm
All chromosomes, the 23 pairs and MTDNA, have STR and SNP
markers. In the testings, paticular
parts of the chromosomes are being tested; thus the base pairs being used have
names and numbers. .
There are many other types of DNA testing. To name a few: Paternity Testing or CODIS
(criminal ID) Testing. Although not typically thought of as a genealogical test, they both aim to identify
relatives through STR testing of autosomal chromosomes.
The test to use depends
on the information you want to find out. I suggest that you join the Newbie DNA
list (YahooGroups). Then ask questions and then decide what test you want
to take. The only real complaints I have seen about genetic genealogy have come
from misunderstanding what a test will revel. So ask questions, decide what
answers you want then decide what test to use.
In addition for the Y
chromosome DNA test.
The first to understand is that to find a Y-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 about 100 – 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 markers.
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
the few hundreds of thousands
years, developed many different
haplogroups. Some are descent and some are lateral developments. That is why a man who has R1b and a man I1b are thousands of
years apart from a common ancestor.
Questions? Ask.. (oh, male haplogroups are named
differently from the 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 and count the reactions (spikes). The amount of
reactions at a particular place (marker) 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
(genetic distance - GD) here is 2, all differences are accumulative. At 37 markers, in my opinion; more then
4-5 steps of difference between two men makes the common ancestor before
of the use of surnames..
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.
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..
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. William
Hurst of the Genealogy-DNA mailing list at rootsweb.com is the local expert.
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 are reported. So in
this case you compare differences.
Now lets discuss the newest testing.. X and autosomal
testing.
First, you inherit atdna from all your past ancestors,
second you might think you inherit 50% from each parent. NOPE but, it averages out 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 even imagined.)
Now here is some additional information from some very
knowledgeable people..
Females have two X chromosomes,
one inherited from the father and the other from the mother, so a
connection 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. If they don't show up in your
list of people you're sharing with, go to Account | Sharing | Example
Profiles. Or create a guest membership.
It
will help you to find the common ancestor by phasing 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 - Ann
Turner
I hope this helps you in understand
testing, and that if you test you enjoy the venture.
Nelda
