Geneaology project
Studies by Genealogists showed that
all of us shared a common ancestor who lived
in Africa approximately 65,000 years ago.
As time passed, our ancestors migrated out
of Africa into the Middle East, Asia, Europe,
North America, and other parts of the world.
During this migration, mutations occurred
in their DNA, and each mutation is linked
to a specific time and place in history.
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.
Y-DNA Haplogroups
Using the results of a Y-DNA marker test,
DNA Ancesty 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.
DNA Ancesty 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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