DNA and Genealogy - How Do They Work Together?

DNA was popularized years ago by using it in high-profile criminal investigations and paternity cases. DNA is commonly used to prove a relationship to an individual. Now DNA is used as a popular tool for determining ancestry. For genealogist this tool has opened more doors into the research area. DNA is passed down from one generation to the next generation; some parts remain almost unchanged, while other parts change drastically. This creates an unbreakable link between generations.

Exactly what is DNA? DNA is material that governs inheritance of eye color, hair color, stature, bone density and many other human and animal traits. DNA is a long, but narrow string-like object. One foot long string or strand of DNA is normally packed into a space roughly equal to a cub 1 millionth of an inch on a side.

Our body's cells each contain a complete sample of our DNA. One cell is roughly equal in size to the cube described in the previous paragraph. There are muscle cells, brain cells, liver sells, blood cells, sperm cells and others. Basically every part of the body is made up of these tiny cells and each contains a sample of DNA identical to that of every other cell within a given person.

There are four, different basic building blocks. Scientists usually refer to these using four letters, A, T, G, and C. Another term for building blocks is the term, "bases." A, T, G, and C are bases. The sequence of bases can code for many properties of the body's cells. The cells can read this code. This is called "coding DNA."

The DNA code, or genetic code as it is called, is passed through the sperm and egg to the offspring. A single sperm cell contains about three billion bases consisting of A, T, G, and C that follows each other in a well-defined sequence along the strand of DNA. Each egg cell also contains three billion bases arranged in a well-defined sequence very similar, but not identical to the sperm.

Now all that aside, what does this tell a genealogist?

It can't tell you your entire family tree or tell you who your ancestors are, but it can tell you:

1. Determine if two people are related.
2. Determine if two people descend from the same ancestor.
3. Find out if you are related to others with the same surname.
4. Prove or disprove your family tree research.
5. Prove clues about your ethnic origin.

DNA test kits can be ordered through the mail or over the Internet at a cost averaging $100-$400 per test. They consist of a cheek swab or mouthwash to easily collect a sample of cells from the inside of your mouth. You send back the sample through the mail and within a month or two you receive the results - a series of numbers that represent key chemical "markers" within your DNA. These numbers can then be compared to results from other individuals to help determine your ancestry.

There are two basic types of DNA tests available for genealogical testing:

1. mtDNA Tests - Mitochondrial DNA is passed by a mother to both male and female offspring without any mixing, so your mtDNA is the same as your mother's mtDNA, which is the same as her mother's mtDNA and so on. It does change very slowly so it cannot determine close relationships as well as it can determine if this is a recent ancestor or one who lived hundreds of years ago.

2. Y Line Tests - Y chromosome in the nuclear DNA is what is being used to establish family ties. The Y chromosomal DNA is only available for males, since the Y chromosome is only passed down the male line from father to son. Tiny chemical markers on the Y chromosome create a distinctive patter, known as haplotype, that distinguishes one male lineage from another. Shared markers can indicate relatedness between two men, though not the exact degree of the relationship. Individuals with the same last name to learn if they share a common ancestor use Y chromosome testing the most.

What can genealogist learn from DNA testing?

1. Link specific individuals - test to see whether you and a person you think may be a cousin, descend from a common ancestor.
2. Prove or disprove the ancestry of people sharing the same last name - test to see if males carrying the CRISP surname are related to each other.
3. Map the genetic origins of large population groups - test to see whether you have European or African American ancestry.

What can a genealogist do with the test results?

Once you submit your DNA sample for testing an exact match in the results between you and another individual indicates that you share a common ancestor somewhere back in your family tree. This ancestor is referred to as your "Most Recent Common Ancestor or MRCA." The results on their own will not be able to indicate who this specific ancestor is, but it can give you help in narrowing down to within a few generations. Genealogist can take this information and work with the individual the DNA matches and try to find the MRCA.