1) The first and earliest DNA to be associated with family trees (doing genealogy) comes through the maternal side...known as mtDNA [name from the mitochondrial structures located out side of the nucleus]. This form of DNA gave rise to a nomenclature called "haplogroups" which were associated with geographic locations.
2) Male descent [Y-chromosome] became the next wave of "genetic" genealogy. As the linear sequence of the DNA contained came to be understood, all labs needed to agree upon the labeling. Broken down by the type of changes that have occurred along this linear arrangement, another series of "haplogroups", divided even further to "haplotypes", became the rave of genealogy. The term MRCA [most recent common ancestor ] was used to calculate a likelihood of sharing a common ancestor based upon the matches shared among folks who had this method of DNA tested.
3) The next phase of genetic genealogy expanded the population base [both male and female] that could be tested. Using techniques that "stained" the surface of the 22 chromosomes called "autosomes", this process gave a map of the staining patterns found associated with the various types of specialized proteins called "histones". This form of testing allowed identification of the geographic locations which clustered these changes. Then, the various markers identified among these autosomes could be assigned to the ethic groups they represented, resulting in the "pie" figure now frequently shown.
A simple diagram follows:
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