[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: .
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: