---
title: "Genetic genealogy"
chunk: 2/3
source: "https://en.wikipedia.org/wiki/Genetic_genealogy"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:14:35.876877+00:00"
instance: "kb-cron"
---

Genetic genealogy has enabled groups of people to trace their ancestry even though they are not able to use conventional genealogical techniques. This may be because they do not know one or both of their birth parents or because conventional genealogical records have been lost, destroyed or never existed. These groups include  adoptees, foundlings, Holocaust survivors, GI babies, child migrants, descendants of children from orphan trains and people with slave ancestry.
The earliest test takers were customers most often those who started with a Y-chromosome test to determine their father's paternal ancestry. These men often took part in surname projects. The first phase of the Genographic Project brought new participants into genetic genealogy. Those who tested were as likely to be interested in direct maternal heritage as their paternal. The number of those taking mtDNA tests increased. The introduction of autosomal SNP tests based on microarray chip technology changed the demographics. Women were as likely as men to test themselves.

=== Citizen science and ISOGG ===

Members of the genetic genealogy community have been credited with making useful contributions to knowledge in the field, an example of citizen science.
One of the earliest interest groups to emerge was the International Society of Genetic Genealogy (ISOGG). Their stated goal is to promote DNA testing for genealogy. Members advocate the use of genetics in genealogical research and the group facilitates networking among genetic genealogists. Since 2006 ISOGG has maintained the regularly updated ISOGG Y-chromosome phylogenetic tree. ISOGG aims to keep the tree as up-to-date as possible, incorporating new SNPs. However, the tree has been described by academics as not completely academically verified, phylogenetic trees of Y chromosome haplogroups.

== Uses ==

=== Direct maternal lineages ===

Mitochondrial DNA (mtDNA) testing involves sequencing at least part of the mitochondrial genome. The mitochondrial DNA is transmitted from mother to child, and so can reveal information about the unbroken maternal line. When two individuals have matching or near matching mitochondrial DNA, it can be inferred that they share a common maternal-line ancestor at some point in the "recent" past. Care should be taken to avoid overstating the recency of a relationship however, as a mutation in the mitochondrial genome will only occur every 1000 to 3000 years on average. For this reason, it is usually impossible to distinguish between two individuals related within the last one or two millennia on the basis of mtDNA alone.

=== Direct paternal lineages ===

Y-Chromosome DNA (Y-DNA) testing involves short tandem repeat (STR) and, sometimes, single nucleotide polymorphism (SNP) testing of the Y-Chromosome, which is present only in males and only reveals information on the unbroken paternal line. As with the mitochondria, close matches with individuals indicate a recent common ancestor. 
A father passes his entire Y chromosome—including the Male-Specific Y (MSY) region—to his son with very minimal change, barring occasional mutations. This region does not recombine with the mother's chromosomes (unlike autosomes and the X), so it is a nearly unshuffled genetic record of direct paternal descent. Y-chromosome lineages can be tracked with a standard phylogeny tree, using traditional data structures and monophylogeny.
Because surnames in many cultures are transmitted down the paternal line, this testing is often used by surname DNA projects.
While early studies using STRs made bold claims that large numbers of men descend from prominent historical individuals (e.g. Niall of the Nine Hostages and Genghis Khan), more recent SNP studies have shown many of these to be invalid. In particular, STR mutations are now known to be largely unreliable in proving kinship, as these mutations can appear in multiple unrelated lineages by chance.
To prove descent from a common ancestor in the male line, a Y-DNA clade requires triangulation back to a most recent common ancestor (MRCA), who is usually referred to by the name of the mutation (e.g. L21, U106, etc.) as a shorthand. A SNP mutation unique to a family or kin group is referred to as a "defining mutation", the testing of which can exclude men not related through the male line within one or two centuries at the most. This has been exploited in recent times to identify the defining mutations of noble and royal lineages, such as the Stewarts of Scotland and the Uí Briúin dynasty of Ireland.