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Genetic Genealogy: DNA and Family History

Modern genealogy combines DNA analysis with traditional documents in order to provide reasonably exhaustive research and more reliable conclusions. This research guide provides tools to unite science with history as you grow your family tree.


Currier & Ives. Family photograph tree. 1871. Library of Congress Prints and Photographs Division.

Genetic genealogy creates family history profiles (biological relationships between or among individuals) by using DNA test results in combination with traditional genealogical methods. By using genealogical DNA testing, genetic genealogy can determine the levels and types of biological relationships between or among individuals.

This branch of genetics became popular in recent years, as costs were drastically reduced and genealogical studies using molecular techniques became accessible to the general public. Advantages of including DNA, as opposed to traditional genealogical research alone, include the ability for researchers to extend their ancestry beyond the paperwork of recent centuries, and to construct ancient pedigrees through molecular evolutionary studies. Genealogists also use DNA to solve mysteries in their immediate families, such as to discover biological parents of adoptees or to determine the accurate male ancestor in a non-paternity event (NPE).

Autosomal, Mitochondrial, and Y-DNA: The Three DNA Tests Used by Genealogists

There are three sources of information in a DNA sample. Y-chromosomal DNA (Y-DNA) is present only in samples from males and gives information on patrilineal descent. Mitochondrial DNA (mtDNA), present in both male and females, gives information on matrilineal descent. Finally, autosomal DNA (atDNA) gives information on both matrilineal and patrilineal descent.

The signal of shared ancestry seen in autosomal DNA is highest in close relatives, but dilutes quickly so that by 5-7 generations of separation, it is difficult to distinguish exact relationships other than shared ethnic affinities. Thus, autosomal DNA (atDNA) is best to help identify ancestors within the most recent 5–7 generations of a family tree.

MtDNA and Y-DNA tests are limited to relationships along a strict female line and a strict male line, respectively. mtDNA evolves rapidly whereas Y-DNA (and atDNA) changes much more slowly. MtDNA and Y-DNA tests are utilized to identify archeological cultures and migration paths of a person's ancestors along a strict mother's line or a strict father's line. Based on MtDNA and Y-DNA, a person's haplogroup(s) can be identified. (A haplogroup is DNA or Chromosomal segments derived from a group of people who share a common genetic ancestor). The mtDNA test can be taken by both males and females, because everyone inherits their mtDNA from their mother, as the mitochondrial DNA is located in the egg cell. However, a Y-DNA test can only be taken by a male, as only males have a Y-chromosome.