Genetic genealogy or DNA testing that supports genealogy became available about a decade ago. Since that time, the companies that offer DNA testing and the types of testing and tools available for analyzing the results have expanded. While a DNA test is a perfectly suitable gift for someone, this article focuses on when to use DNA testing to support genealogy projects. You don’t have to know what DNA is made of or be a scientist to use DNA results effectively in your genealogy. You do however, need to understand the types of DNA, basic inheritance paths, and the uses of DNA for genealogy.
Types of DNA
There are three types of DNA: Y- DNA, autosomal DNA, and mitochondrial DNA.
- Y-DNA is the male sex chromosome. While Y-DNA does mutate over time, it is relatively stable and does not recombine. Y-DNA is used for surname studies and can show both recent and deep ancestral relationships.
- Autosomal DNA (sometimes written as at DNA) recombines each generation. Autosomal DNA can be used to match relatives when the common ancestor is no more than around nine generations back. Any further back and the DNA will have recombined too many times and DNA matches are much less likely. The amount of overlapping DNA indicates the relationship between two individuals. The greater the overlap, the closer the relationship.
The X chromosome is a special type of autosomal DNA that recombines and is the second type of sex chromosome.
- Mitochondrial DNA (sometimes written as mt DNA) is extra-nuclear, that is, it is located outside of the nucleus of the cell. This type of DNA does not recombine and has low mutation rates. It is used to track maternal relationships, both near term, and as well as deep ancestral relationships.
Inheritance
The DNA of a person is referred to as his or her genome.
- We all inherit roughly half of our autosomal DNA from each of our biological parents. Your parents, in turn, inherited half of their DNA from each of their parents. Logically, that would mean that you inherited one-quarter of your DNA from each of your biological grandparents and one-eighth of your DNA from your biological great grandparents.
- Y-DNA is only passed from father to son.
- The mitochondrial DNA is passed from mother to her children, regardless of the child’s sex.
- An X chromosome is passed from the mother to both male or female children and from father only to his female children.
Uses of DNA for Genealogy
DNA testing can be an invaluable tool, particularly for adoptees and others with unclear parentage. To maximize the use of the DNA results, you should keep in mind what question(s) you are trying to answer and undertake testing that answers those questions. You need to select the appropriate company and type of test for the results that will most help you. Don’t be driven by special prices for testing. For example, Ancestry only offers autosomal DNA testing. If you are wanting Y-DNA or mitochondrial DNA tests done, testing at Ancestry would not be useful. It is also advisable, if you plan to use more than one testing company for a project, to have a strategy on how the results will be put into one system for comparison. Some companies do allow you to transfer data. Check with the company in advance.
DNA can help you:
- Determine your ethnicity and examine how your family may have migrated across continents and oceans
- Participate in surname or other studies
- Examine what DNA was inherited from parents, grandparents, etc.
- Solve unknown or misattributed parentage
- Validate or disprove records that you may have collected
- Validate or disprove relationships that you hypothesized based on records
- Find new cousins or reconnect you with relatives you may or may not have known about
- Identify errors in a pedigree chart
- Potentially identify health traits that may be of interest
Above all, if you undertake DNA testing, you need to be prepared for the unexpected.
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