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DNA is the carrier of our genetic information, and is passed down
from generation to generation. All of the cells in our bodies, except red
blood cells, contain a copy of our DNA.
At conception, a person receives DNA from both the father and mother. We
each have 23 pairs of chromosomes. Of each pair, one was received from
the father and one was received from the mother. These 23 pairs of
chromosomes are known as nuclear DNA because they reside in the nucleus
of every cell (except red blood cells).
The 23rd chromosome is known as the sex chromosome. As with the other
chromosomes, one is inherited from the father, and one from the mother.
The 23rd chromosome from the mother is always an X. From the father, a
person either inherits an X chromosome or a Y chromosome. The chromosome
inherited from the father determines their gender. An X from the father
would result in an XX combination, which is a female, and a Y from the
father would result in an XY combination, which is a male.
 
We also inherit our mitochondrial DNA (mtDNA) from
our mother, and none from our father. mtDNA is located outside the
nucleus of the cell.
DNA is made up of four bases: adenine (A), cytosine
(C), thymine (T), and guanine (G). The order of these bases is called the
DNA sequence.
Whenever a particular base is present on one side, its
complementary base is found on the other side. In the example above, see
how the bases always occur in complementary pairs. Guanine (green) always
pairs with cytosine (red) and thymine (yellow) always pairs with adenine
(blue). So we can write the DNA sequence by listing the bases along
either one of the two sides. In the example shown, one side reads:
T G T T C G T C etc.
For Genetic Genealogy, which is the application of DNA testing to
genealogy research, two types of DNA can provide information useful in
conjunction with genealogy research. These two types are the Y chromosome
and mtDNA. The areas that we test are found in the so-called “Junk DNA”
of the Y chromosome and mtDNA because it is found between the genes.
Y DNA
The Y chromosome is transmitted from father to son. Testing the Y
chromosome provides information about the direct male line, meaning the
father to his father and so on. The locations tested on the Y chromosome
are called markers. Occasionally a mutation occurs at one of the markers
in the Y chromosome. Mutations are simply small changes in the DNA
sequence. They are natural occurrences and take place at random
intervals. Overall, they are estimated to occur once every 500
generations per marker. Mutations can sometimes be valuable in
identifying branches of a family tree.
Each marker has a name assigned to it by the scientific community, such
as DYS#391, DYS#439 or GATA H4. The scientists classify these markers as
Short Tandem Repeats (STR) because at each of these marker locations a
short DNA code repeats itself. The result for a marker is the number of
times the code repeats at that location and is called the allele value.
The result received for a Y-DNA test is a string of allele values called
a “haplotype.” Here is an example of a 25-marker haplotype:
|
Locus
|
DYS#
|
Alleles
|
|
|
|
1
|
393
|
13
|
|
2
|
390
|
24
|
|
3
|
19*
|
14
|
|
4
|
391
|
11
|
|
5
|
385a
|
11
|
|
6
|
385b
|
14
|
|
7
|
426
|
12
|
|
8
|
388
|
12
|
|
9
|
439
|
12
|
|
10
|
389-1
|
13
|
|
11
|
392
|
13
|
|
12
|
389-2
|
29
|
|
13
|
458
|
17
|
|
14
|
459a
|
9
|
|
15
|
459b
|
10
|
|
16
|
455
|
11
|
|
17
|
454
|
11
|
|
18
|
447
|
24
|
|
19
|
437
|
15
|
|
20
|
448
|
19
|
|
21
|
449
|
30
|
|
22
|
464a**
|
15
|
|
23
|
464b**
|
15
|
|
24
|
464c**
|
17
|
|
25
|
464d**
|
17
|
*Also known as DYS 394 **On 5/19/2003,
these values were adjusted down by 1 point due to a change in Lab
nomenclature.
Family Tree DNA offers 5 Y chromosome tests:
12-Marker
37-Marker
67-Marker
Backbone Haplogroup
Deep-SNP Test
|
First 12 Markers
|
Additional 25
(to 37 markers)
|
Additional 30**
(to 67 markers)
|
|
Locus
|
DYS#
|
|
1
|
393
|
|
2
|
390
|
|
3
|
19*
|
|
4
|
391
|
|
5
|
385a
|
|
6
|
385b
|
|
7
|
426
|
|
8
|
388
|
|
9
|
439
|
|
10
|
389-1
|
|
11
|
392
|
|
12
|
389-2
|
|
|
Locus
|
DYS#
|
|
13
|
458
|
|
14
|
459a
|
|
15
|
459b
|
|
16
|
455
|
|
17
|
454
|
|
18
|
447
|
|
19
|
437
|
|
20
|
448
|
|
21
|
449
|
|
22
|
464a
|
|
23
|
464b
|
|
24
|
464c
|
|
25
|
464d
|
|
26
|
460
|
|
27
|
GATA H4
|
|
28
|
YCA II a
|
|
29
|
YCA II b
|
|
30
|
456
|
|
31
|
607
|
|
32
|
576
|
|
33
|
570
|
|
34
|
CDY a
|
|
35
|
CDY b
|
|
36
|
442
|
|
37
|
438
|
|
|
Locus
|
DYS#
|
|
38
|
531
|
|
39
|
578
|
|
40
|
395S1a
|
|
41
|
395S1b
|
|
42
|
590
|
|
43
|
537
|
|
44
|
641
|
|
45
|
472
|
|
46
|
406S1
|
|
47
|
511
|
|
48
|
425
|
|
49
|
413a
|
|
50
|
413b
|
|
51
|
557
|
|
52
|
594
|
|
53
|
436
|
|
54
|
490
|
|
55
|
534
|
|
56
|
450
|
|
57
|
444
|
|
58
|
481
|
|
59
|
520
|
|
60
|
446
|
|
61
|
617
|
|
62
|
568
|
|
63
|
487
|
|
64
|
572
|
|
65
|
640
|
|
66
|
492
|
|
67
|
565
|
|
*Also known as DYS 394
** The 29 markers on this third panel have mutation rates that have yet
to be determined.
The markers in red have been
observed to have a faster-than-average mutation rate, and therefore these
markers are very helpful at splitting lineages into subsets or branches
within your family tree.
Surname Project
A Surname Project is a project which is established to test and compare
those with a common surname and variants. A Surname Project has a leader
known as the Group Administrator. This person assists the members with
understanding their results, typically interprets the results for the
group, and may publish this information in a newsletter or web site.
There are a wide variety of applications for Y-DNA testing. Y-DNA testing
can be used to confirm the paper genealogical research for your family
tree. It can determine which family trees with the same or variant
surnames are related, and can provide clues to help you with your
genealogy research. These are just a few of the applications for Y-DNA
testing.
Since the Y chromosome is only found in men, those who take the Y-DNA
test must be males. For females who are interested in the Y-DNA result
for their surname or family tree, a close male relative with that surname
would need to provide the sample.
Y-DNA Haplogroups
Using the results of a Y-DNA marker test, Family Tree DNA estimates the
tester’s haplogroup. The haplogroup identifies the person's major
population group and provides information about the ancient origin of the
male line. Family Tree DNA also offers a haplogroup test which
participants can use to confirm their haplogroup assignment. The
“Backbone” haplogroup test confirms the base haplogroup assignment, and
the “Deep Clade” haplogroup test identifies the branch of the haplogroup
the person belongs to.
mtDNA
mtDNA is passed
from mother to child. Since only females pass on their mtDNA, testing the
mtDNA tells about the mother, to her mother, and so on along the direct
maternal line. Both males and females receive mtDNA from their mothers,
so both men and women can test their mtDNA.
While mutations occur in mtDNA, the rate of mutation is relatively slow.
Over thousands of years these mutations build up so that one female line
will have a sequence distinguishable from another. As people spread
throughout the world, mutations occasionally occurred in different
populations over time. This allows us to test the mtDNA to identify the
world origin of a person’s lineage.
mtDNA is tested and the result is compared to a reference sequence called
the Cambridge Reference Sequence (CRS). By comparing an mtDNA sequence to
the CRS, we can identify the ancient lineage to which you belong, called
the haplogroup. Many haplogroups are continent-specific and some of their
branches are region-specific.
mtDNA Haplogroups
Haplogroups are labeled alphabetically. Today, anthropologists have
identified certain haplogroups that originated in Africa, Europe, Asia,
the islands of the Pacific, the Americas, and sometimes particular ethnic
groups. Of course, haplogroups that are specific to one region are
sometimes found in another, but this is due to more recent migration.
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