General Information about DNA Relationships
Compiled from information published by the
Sorenson Molecular Genealogy Foundation, DNA.Ancestry.Com., and other sources.
Molecular Genealogy: Analyzing DNA can allow people to find their cousins who may be connected across generations and around the world. This endeavor is sometimes called Molecular Genealogy. Here is some basic information about Molecular Genealogy:
Cells, Chromosomes and DNA: DNA is found in every cell in your body except red blood cells. In the center of each cell is a membrane called a nucleus. A nucleus contains chromosomes, and chromosomes are made up of long strands of DNA which contain all the body's genes. (Genes are the functional units of DNA.) Humans have a total of 46 chromosomes, which are grouped into pairs. Each of the 23 pair consists of one chromosome from our mother and one from our father. In females the 23rd chromosome pair consists of two X-chromosomes. Males, however, have an X-chromosome and a Y-chromosome. Therefore, it is the Y-chromosome that determines male gender.
Y-DNA: The male Y-chromosome is one of the most useful chromosomes in genealogical studies, because it has the unique property of being passed virtually unchanged from generation to generation. This means that a man and all his sons will have the same (or similar) Y-chromosome, and that males with a common paternal ancestor have similar Y-DNA.
mtDNA: DNA can also be found in the mitochondria of the cell, which is responsible for producing energy to perform all cellular functions. The mitochondrial DNA-called mtDNA--follows the direct maternal line. Women pass their mtDNA to all of their children, but then only their daughters will pass it on to the next generation. This makes mtDNA useful for tracing one's direct maternal line.
Markers: Y-chromosome contains 59 million bits of information, each of which is encoded by a "base pair." Looking at all of these base pairs is impractical, so geneticists have identified a number of specific chromosome locations that can be used for analysis and comparison. These unique locations are called "markers". In some ways, DNA marker values are like telephone numbers, and because telephone numbers may appear in different cities but belong to unrelated people, it is advantageous for scientists to test many different DNA markers to avoid possible ambiguity. Generally, the more markers tested, the easier it is to distinguish individuals and family tree branches. Currently, some scientists believe that 36 markers are a sufficient number of Y-chromosome markers to be tested for most molecular genealogical research purposes. Also, it has been found that individuals who share exact genetic DNA marker values also share a common ancestor, and the closer the match in marker values the more recently one's common ancestor may have lived. However, because of the extrapolative and statistical nature of molecular genealogy, it is sometimes difficult to predict how far in the past common ancestors may have lived without the genealogical information found in reliable pedigree charts.
Non-Relatedness: DNA tests sometimes suggest that people who once thought they were related are not so related. Such an unexpected finding of "non-relatedness" may reflect an adoption, an altered or assumed surname, an illegitimate birth, or maternal infidelity somewhere in the ancestral line. In addition, one must keep in mind that the science of molecular genealogy is relatively young, and there is still much that scientists are learning about human ancestry and its migrations over time, unusual DNA anomalies, and the extrapolation of specific ancestral relationships through DNA.
What If Your DNA Test Does Not Support Your Genealogical Assumptions? Suggestion: Always remember that "Family is family, whether it is by blood, adoption or inheritance." If DNA testing does not support your genealogical assumptions, do not distance yourself from those who have supported and loved you during your life. Regardless of how you received or acquired your surname--whether it was by blood, adoption or inheritance--stay close to those who know and love you, and invest in strengthening family ties that connect you to those you call and know as "family".