Introduction to Genetic Genealogy
There are two types of DNA tests used for genealogical studies:
-
Y-chromosome (Y-DNA): This test makes use of the Y-chromosome.
Females have two X-chromosomes, while males have one X-chromosome
and one Y-chromosome. It's the Y-chromosome that passes from father
to son, making it invaluable in studying male-to-male lineage.
-
Mitochondrial (mtDNA): The other method utilizes mitochondrial
DNA (mtDNA), which is passed by a mother to both male and female offspring.
A match between the mtDNA of a male potential relative and a female's
mtDNA would mean the two have a common female ancestor. A male's mtDNA
comes only from his mother and is not passed on to his offspring.
Since we're presently interested in tracing the Arnold (and variant)
surname - which is usually passed from father to son - this study will
use the Y-DNA method.
Even though the Y-DNA method will be used (and therefore only males
will be tested), females are still encouraged to get involved. How?
By letting someone else know about the study, or even ordering a test
kit for that person.
There are several options for the Y-DNA test. The difference lies in
how many markers are evaluated, which determines the usefulness of the
results.
-
The 12-marker test compares 12 markers from your results to the same
12 markers of other participants. This allows you to identify the
likelihood that you and another participant share a common ancestor.
This likelihood is measured in the number of generations back to the
most recent common ancestor, or MRCA.
-
In a similar fashion, 25-, 37- and 67-marker tests look for matches
between you and other participants. However, by comparing a greater
number of markers, you get a more exact estimate of the number of
generations required to find the MRCA.
Here's a chart that shows how increasing the number of markers can decrease
the number of generations needed to get back to the MRCA..
|
Number of matching markers
|
50% probability
|
90% probability
|
95% probability
|
|
that the MRCA was no further back than this number
of generations
|
|
10 of 12
|
16.5
|
56
|
72
|
|
11 of 12
|
17
|
39
|
47
|
|
12 of 12
|
7
|
23
|
29
|
|
23 of 25
|
11
|
23
|
27
|
|
24 of 25
|
7
|
16
|
20
|
|
25 of 25
|
3
|
10
|
13
|
|
35 of 37
|
6
|
12
|
14
|
|
36 of 37
|
4
|
8
|
10
|
|
37 of 37
|
2 to 3
|
5
|
7
|
|
65 of 67
|
6
|
12
|
14
|
|
66 of 67
|
4
|
8
|
9
|
|
67 of 67
|
2
|
4
|
6
|
|
|
As you can see, the higher-marker tests offer a much greater potential
of establishing an MRCA in fewer generations.
For a more complete tutorial on genetics, DNA, etc., the Blair surname
study has a fantastic tutorial called DNA
101. Thanks to John Blair for allowing us to link to his site.
How does the study work? >>
|
Arnold DNA Study
