The distinction between your genealogical family tree and your genetic family tree is important when it comes to analyzing your DNA test results. Understanding the difference between these two groups of relatives—and noting where they overlap—can often make or break your genetic genealogy strategy:
Genealogical family tree
This includes all your direct-line ancestors who had a child who had a child who had a child, and so on, ultimately leading to you: your two parents, your four grandparents, your eight great-grandparents, etc. This is the tree you research in historical records, such as birth and death certificates, census records and newspapers. Many genealogists find that the paper trail ends or becomes much more difficult to identify before the 1700s or 1800s, making it difficult to fill in beyond that point.
Genetic family tree
This tree contains only those ancestors that contributed to your DNA. A parent passes on only about 50 percent of his DNA to his children. As a result, pieces of DNA are lost with each generation, and so not every person in your genealogical family tree contributed a segment of his or her DNA sequence to your DNA sequence. Five to seven generations back, ancestors on your genealogical family tree are no longer reflected in your genetic family tree, as shown by the white spaces in the family tree fan chart below.
Knowing that someone who appears in your genealogical family tree may not appear in your genetic family tree is crucial to understanding your test results.