[continued from Part 1]
The Y-chromosome is only carried by males and is inherited in a line of direct paternal descent. A male receives his Y-chromosome from his father who inherited it from his father, and on and on. Occasional mutations help to distinguish different Y-chromosome lineages. Because surnames are often inherited in a similar pattern in many cultures, two individuals with the same surname and similar Y-chromosome signatures share a common direct line paternal ancestor. Likewise, two individuals with different surnames but who share the same Y-chromosome signature share a common direct line paternal ancestor. This situation may be indicative of a “non-paternal event (NPE),” which could include an undocumented adoption, illegitimacy, a surname change, or any number of other situations which might result in the paternal surname not being passed to both lines of descent.
Mitochondrial DNA is carried by both males and females, but it is
only passed on by females. Therefore, mitochondrial DNA is inherited along the
direct maternal line. An individual receives their mitochondrial DNA from their
mother who received it from her mother. Occasional mutations help to
distinguish different mitochondrial DNA lineages. If two individuals share a
mitochondrial DNA signature it may be indicative of shared maternal ancestry.
Because mitochondrial DNA is much smaller than any other type of DNA, and
because it undergoes fewer mutations over time, it is harder to make
genealogical discoveries with this type of test. It is best used to offer
support for genealogical hypotheses.
Autosomal DNA tests analyze portions of the DNA that are inherited
both paternally and maternally. Each person receives half of their autosomal
DNA from their mother and half from their father. Autosomal DNA undergoes a
process called recombination, which shuffles the maternally and paternally inherited
copies of DNA before passing them on to the next generation. Each person
receives exactly half of their autosomal DNA from each parent, but only
approximate percentages can be applied to more distant generations of ancestors
due to the random nature of recombination. Each individual shares about 25
percent of their DNA with each grandparent and half that amount for each
subsequent generation. Individuals who share large identical segments of
autosomal DNA most likely share a recent common ancestor.
The X-chromosome is one other type of DNA that has a unique
inheritance pattern. Males have one X-chromosome from their mother. Females
have two X-chromosomes: one from their mother and one from their father. The
X-chromosome undergoes recombination in females, but not in males. Though the
X-chromosome cannot be assigned to a specific line of descent, it can be used
to eliminate individuals from a person’s tree as possible common ancestors to
their matches. The X-chromosome is tested at each of the companies as part of
their autosomal DNA tests.
Reasons to Test
Genetic genealogy tests can help confirm or refute genealogical
hypotheses, open up new avenues of research, or they may not be helpful at all.
However, as the databases grow and as more people test, the last result in this
list is becoming increasingly uncommon.
DNA testing can be useful for answering questions regarding
adoption, illegitimacy, unknown or mis-attributed parentage, name changes,
immigration, and many other instances of difficult-to-trace ancestry.
While DNA tests have the ability to help investigation in these
difficult situations, they also have the ability to reveal well-kept family
secrets. Whenever a DNA test is taken, the subject should recognize the
possibility of discovering previously unexpected relationships through
undocumented adoptions and illegitimacies. Many times the discovery of these
events can be surprising and may drastically change the way you view and
approach your family history. Testing companies and private researchers do not
claim responsibility for these discoveries and the impact that they may
have on individuals and families.
Genetic Genealogy Success
Many adoptees have successfully identified their birth parents
through genetic testing and other available resources. However, genetic testing
can also be helpful for genealogical questions. Many have successfully used
Y-DNA testing in conjunction with autosomal DNA and the historical record to
identify fathers of illegitimate ancestors. Others have used autosomal testing
to overcome recent genealogical brick walls. Yet others have used mitochondrial
DNA to support descent from common maternal ancestors and to confirm or refute
family legends regarding African or Native American ancestry.
In one recent case, we were able to reveal the identity of a
client’s 2nd great grandfather through autosomal testing. A
concealed illegitimacy had prevented previous contact with this part of the
client’s family and as a result of DNA testing, we were able to extend the
client’s ancestry several generations. Though we were able to answer the
client’s research question, this research also opened new avenues of investigation
since no member of the family has yet been able to determine the origin and
parentage of their common 2nd great-grandfather who was born in
the early 1850s in Missouri. DNA testing and collaboration with these newfound
cousins may help to reveal this individual’s ancestry through future research.
Applications of DNA testing to genealogical investigation are many
and varied, and they are also frequently successful. However, even when tests
do not yield immediate results, as more people test and more matches are
identified, genetic genealogy tests become sources that keep giving.
NOTE: Legacy Tree Genealogists is not affiliated with any of the
companies mentioned in this blog post. However, our resident DNA experts would
be happy to help you analyze and make sense of the results you get from any of
them. Give us a call or drop us an email and let us know how we can help
you: https://legacytree.com/contact-us.
Legacy Tree Genealogists is the
world's highest client-rated genealogy research firm. Founded in 2004, the
company provides full-service genealogical research for clients worldwide,
helping them discover their roots and personal history through records,
narratives, and DNA. For more information on Legacy Tree and their services,
visit: www.legacytree.com
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