Genetic genealogy is a modern tool for family historians that allows us to study our biological heritage through DNA. Genetic genealogy has been utilized by scientists and historians since 1994. Early DNA testing became available to family historians in 2000. I was on the waiting list for Ancestry.com's DNA test and I was among the first to receive the test when it was launched in 2012.
DNA is short for "deoxyribonucleic acid." It is a component of every cell in our bodies, and it carries the instructions for life. DNA controls the vast majority of functions for our bodies' cells and is found in the cell's nucleus.
DNA molecules are made up of nucleotides. There are four different nucleotides: adenine, cytosine, guanine, and thymine. Two strings of nucleotides intertwine to form a single double-helix structure called a chromosome. Humans have twenty-three pairs of chromosomes. We inherit one copy from each parent. Therefore, we have forty-six chromosomes and ninety-two strings of nucleotides in total.
In addition to the DNA in the nucleus, small circular strands of DNA are found within mitochondria outside of the nucleus. I have written more about mitochondria in other blog posts. Mitochondrial DNA (known as mtDNA) can also be used for genetic genealogy.
Most commercial DNA tests examine autosomal DNA (atDNA). This is the test that I did through Ancestry.com back in 2012. Twenty-two of our chromosomes are known as "autosomes" and one is known as a "sex chromosome" (i.e. the Y or X chromosome). Autosomal testing looks specifically at the autosomal DNA. Since one copy of each chromosome is inherited from each parent, the atDNA test reveals information about both paternal and maternal lines, which is not the case for mtDNA and/or sex chromosome testing.
Since only about 50% of our DNA is passed down to our children, some DNA is lost with each generation. We are almost guaranteed to carry DNA from our parents, grandparents, and great-grandparents; however, it is much less likely with each generation that every person in the genealogical family tree contributed a piece of their DNA to the test taker's DNA. Because of this, your "genetic family tree" is a subset of your genealogical family tree and contains only those ancestors who contributed to your DNA. Similarly, you are a subset of your parents' genetic family tree since you have only inherited about 50% of each of your parents' DNA. You will share each of your true genetic matches with one (or both) of your parents, but your parents may or may not share each of their genetic matches with you.
For Christmas this year, I finally purchased DNA testing kits for both of my parents as well as my maternal grandparents. Although I originally thought testing just myself was adequate, I realized that 50% of the previous generation can be lost if only one person tests. If you can test your parents or grandparents, you can regain the 50-75% that may otherwise be lost. We are still awaiting the results, but I'm excited to see if there are any new discoveries to be made!
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