Types of DNA to Test for Family Research:
Three types of DNA can be tested for genealogy purposes: (1) autosomal DNA, (2) Y-DNA, and (3) mitochondrial DNA. Each of these types of DNA and their uses in genealogy is explained below.
Each person receives half of their autosomal DNA (atDNA) from their mother and half from their father. DNA is arranged in chromosomes. Each person has 22 pairs autosomal chromosomes, 1 pair from their mother and 1 pair from their father.
In addition to the autosomal chromosomes, each person has a set of sex chromosomes. Males receive a Y chromosome from their dads and an X chromosome from their moms. Females receive one X chromosome from their dads and one X chromosome from their moms. Some DNA testing companies analyze the X chromosome with the atDNA test.
atDNA is said to be blended. That is, each chromosome from a parent is a mixture of their parent’s DNA, that is, the grandparents. This blending is due to a process called recombination. When eggs and sperm are formed, each chromosome in the parent pairs up and exchanges segments of DNA. This results in a recombined chromosome. The result is that the chromosomes the parents give a child is a mixture of the child’s grandparents’ chromosomes.
The illustration below shows atDNA recombination. The arrows highlight how part of the purple chromosome, which is present in one grandmother, gets transferred to the mother. The mother then has three children, two of which inherit a portion of the purple chromosome.
Testing atDNA gives you a look at your maternal and paternal relatives. It can be used to find close relatives, e.g., parents, siblings, half siblings, cousins, and more distant relatives, e.g., 4th cousins, great grandparents. In general, atDNA testing covers 5-8 generations.
atDNA matches are from the company’s database where you tested. There are three companies used for genetic genealogy: Ancestry, FamilyTreeDNA (FTDNA), and 23andMe. Thus, if you test at FTDNA, your match list will only include people who’ve also tested at FTDNA.
atDNA also provides an ethnicity estimation. This is because certain DNA mutations arose in specific populations. These mutations are passed down through the generations. Ethnicity reporting by some companies can reflect the ethnicity of your ancestors a long time ago. For example, Ancestry’s ethnicity estimates are said to show your ancestors’ ethnicity 500-1000 years ago. 23andMe’s ethnicity estimates are said to show your ancestors’ ethnicity closer to 500 years ago. FTDNA’s ethnicity estimates are in between the two companies’ estimates
atDNA can be tested in both male and females. It’s oftentimes a good place to start your DNA testing.
The second type of DNA for family research is Y-DNA. This kind of DNA is passed only from fathers to sons. Because of this inheritance pattern, Y-DNA can be used to trace a patrilineal line, that is, one’s father’s father’s father’s (etc.) line. Y-DNA is useful for genealogy purposes to learn more about your patrilineal line. Results from testing Y-DNA can sometimes provide a patrilineal surname or determine the ethnicity of a lineage.
Y-DNA might also be used to determine on which side of a family someone is. However, everyone’s father has both his own father and mother. Therefore, just because someone doesn’t match your Y-DNA type, doesn’t mean that the person isn’t on your father’s line. That person might be on your dad’s mom’s line.
Because Y-DNA is passed only from fathers to sons, only males can have Y-DNA tested. However, a female can test male relatives to determine the Y-DNA type(s) of their family. For example, a brother’s Y-DNA test result would show her father’s Y-DNA type of that lineage. A maternal uncle’s Y-DNA test result would reflect her maternal grandfather’s Y-DNA type of that lineage.
Just remember, your Y-DNA results reflect only one part of your father’s line: your father’s father’s father’s (etc.) line.
The third type of DNA for family research is mitochondrial DNA (mtDNA). mtDNA is passed only by mothers. However, it is passed to all children–regardless of their gender. Since mtDNA is inherited in this way, mtDNA can be used to trace a matrilineal line, that is, one’s mother’s mother’s mother’s (etc.) line. mtDNA is useful for genealogy purposes to learn more about your matrilineal line. Results from testing mtDNA can sometimes determine the ethnicity of a lineage.
mtDNA might also be used to determine on which side of a family someone is. However, everyone’s mother has both her own mother and a father. Therefore, just because someone doesn’t match your mtDNA type, doesn’t mean that the person isn’t on your mother’s line. That person might be on your mom’s father’s line.
Because mtDNA is passed from mothers to all children, anyone can have their mtDNA tested. Just remember, your mtDNA results reflect only one part of your mother’s line: your mother’s mother’s mother’s (etc.) line.
Summary – Types of DNA for Family Research
As you can see, the type of DNA to test depends on (1) your gender and the gender of the person(s) you are researching and (2) what you’re trying to determine.