DNA Basics

Genetic Genealogy Overview

What can DNA do for me?
You might already be familiar with how DNA testing can help solve crimes, confirm the paternity of children, and even determine the identity of ancient mummies. Now DNA can also help you with your genealogical research. It's a simple and painless process to gather your DNA sample and within a few weeks have results that you can compare with the ever-expanding Ancestry.com DNA database to find potential genetic cousins. Learn more about the science behind DNA, chromosomes, and genetics.
DNA Testing by Megan Smolenyak
Finding genetic cousins
By comparing your Ancestry.com DNA test results with others, you can determine to what extent you are related. For example, the more closely your result set matches another's, the narrower the range of generations between the two of you and your common ancestor.
As the Ancestry.com DNA database grows, we will automatically compare your result against each new entry. If a close match is found, you will receive an e-mail with a link to a page that describes how your two test results match. You can now begin communicating with your genetic cousin using Ancestry.com's Connection Service as the first step towards comparing the genealogies of your two families.
Discover ancient ancestry
In addition to finding genetic cousins, your DNA test can also reveal your ancient origins. Beginning over 170,000 years ago, our ancient human ancestors migrated out of Africa and began their slow and steady spread across the continents. Over time as these ancestors spread throughout the world and adapted to their new surroundings and environments, their DNA diversified and they became genetically distinct from one another. Today, these differences can be traced through DNA and provide insights on how your ancient ancestors migrated and diversified into distinct populations.

What is DNA and Genealogy

All humans have 23 pairs of chromosomes, including a pair of sex chromosomes, known as "X" and "Y". Males have both an X- and a Y-chromosome (with the Y-chromosome inherited from the father) while females have two X-chromosomes (one X-chromosome inherited from each parent.) Genetic Genealogy is interested in heritage markers or the area of the chromosome which reveals family relatedness.

Because the Y-chromosome is passed essentially unchanged from father-to-son, it provides genetic genealogists with a powerful tool for tracing a paternal lineage. Specific portions of the Y-chromosome are analyzed and compared against other participants' Y results to determine the relatedness between the two participants.
Since both parents contribute X-chromosomes to their daughters, a different source of DNA must be used to trace the maternal line. Mitochondrial DNA (mtDNA) is inherited by both male and female children exclusively from their mothers and provides insight into one's maternal lineage. (Learn more about mitochondrial DNA.)

What Ancestry.com DNA Testing Cannot Do

The type of testing performed by Ancestry.com DNA is limited to areas of DNA that have the greatest application to genealogy which reveal insight into family relatedness. The portion of DNA tested is within the non-coding regions and do not provide distinguishing information about an individual such as hair color.
While DNA testing in general has a promising future as a tool for predicting one's chances for developing disease such as diabetes, Alzheimer's, and cancer; Ancestry.com DNA does not perform medical diagnostic testing on any of its DNA samples.
A common application of DNA testing is in determining the paternity of a child for custody or inheritance. Results of a Ancestry.com DNA test can definitively disprove a genetic relation. A large number of mismatches between two test results reflects that the two participants are not directly related. A 100% match, on the other hand, cannot be used as legal proof of paternity, but can serve as a strong indication.


Ancestry.com DNA protects your privacy by allowing you to make your DNA results anonymous. Doing so hides your Ancestry.com username, but allows your DNA results to still be matched with others in the Ancestry.com DNA database. So even if you have chosen to keep your username hidden, you can still discover genetic cousins and, if the match is close enough, contact them safely and anonymously.

Connection Service
Your privacy is also protected by using Ancestry.com's Connection Service to contact other DNA participants. The Connection Service allows you to send an e-mail to a potential genetic relative without revealing your own e-mail address. Instead, the message is sent through Ancestry.com and the system transfers the message to your e-mail address without revealing your actual address. Replies can also be made through the Connection Service until you feel you wish to make direct e-mail contact with the other party.

How do I collect a sample?

Collecting a DNA sample is easy and painless. Simply swab the inside of your mouth to collect cheek cells and return the swabs to Ancestry.com DNA. Within a few weeks, your results will be ready. No blood sample needed!

Shortly after you confirm your order, you'll receive an e-mail indicating that your test kit has been sent. In a few days, you should receive your personalized kit which contains:

Step 1 - Prepare to Collect DNA Sample
Included in each DNA Collection Kit, is a form printed on the Collection Envelope to be completed by the participant (person providing the DNA sample.)
Before you collect the sample, make sure you have waited at least 30 minutes from your last meal or snack to help reduce sample contamination.
Step 2 - Collect DNA Sample
  • Open the Swab Packet and remove one swab. Leave the other swabs in the sterile package until ready for use.
  • Holding only the stick portion (do not touch the swab area), rub the swab up and down the inside left wall of your mouth. Vigorously scrape the inner left cheek using a vertical, up-and-down motion. Rotate the swab while scraping the inner cheek surface. Do this for a minimum of 30 seconds.
  • Place swab directly into the Collection Envelope. Do NOT put it back into the Swab Packet. Do NOT touch the swab area to any other surface.
  • Repeat steps A and B with the remaining two swabs in the Swab Packet, swabbing the inner right cheek with one of the swabs and the inside front of the mouth with the other.
  • This kit is for one individual only. The same person must use all three swabs.
  • Do NOT return samples from more than one person in a single envelope.
  • We recommend leaving the Collection Envelope open for about 30 minutes after collection to allow the samples to dry before sealing the envelope.
Step 3 - Mail the DNA Collection Kit
Once the swabs have dried, carefully place them into the Collection Envelope and enclose this envelope into the pre-addressed mailing envelope. If you are mailing from outside of the United States or Canada, please place the appropriate postage on the envelope.
You will receive an e-mail notification when the lab receives your DNA sample, and again when your DNA results are available. It only takes a few weeks for the lab to process your DNA and make your results available.
Once your test results have been entered into the system, Ancestry.com DNA will continually look for people who have similar DNA results so that you might find your long lost genetic cousin.

The Science Behind Genetic Genealogy

The following sections provide an overview of the science behind DNA and genealogy. It will familiarize you with some of the technical terms commonly used in the field of genetic genealogy.
DNA is found in every cell in your body except the red blood cell. It is located in the center of the cell in a membrane called the nucleus. DNA contains all the information necessary to coordinate the functions of your body from wiggling your toes to operating your heart. That's a lot of information! A typical animal cell contains one meter of DNA. Written in a linear alphabet of four letters, the genetic information carried in a human cell could fill a book of more than 500,000 pages! But how is that much information packaged?
DNA is tightly wrapped in configurations known as Genes, which are the functional units of DNA. Genes provide provide the instructions for life. The human genome is estimated to contain 30,000 to 40,000 genes.
Only about 2% of the human genome contains genes; the remainder consists of non-coding regions, whose functions vary from providing structure to the chromosome, to having no detectable purpose. It is these non-coding segments that are being compared for genealogical purposes.
Humans have a total of 46 chromosomes, which are grouped into pairs. Each of the 23 pairs 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. It is, therefore, the Y-chromosome (Ycs) that determines the male gender. It is also the Y-chromosome (Ycs) that is one of the most useful chromosomes in genealogical studies. The Y-chromosome 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. Likewise, he will have the same Y-chromosome as his father and grandfather and so on. This gives the Y-chromosome the unique property of following the surname, in most cases, which makes it a very valuable genealogical tool.
In addition to DNA found within the nucleus of the cell, DNA can also be found in the mitochondria of the cell. The mitochondria is the power house of the cell. It is responsible for producing energy to perform all the cellular functions. The mitochondrial DNA (mtDNA) follows the direct maternal line. Women pass their mtDNA to all of their children, but then only the daughters will pass it on to the next generation.
DNA itself is a helical structure, similar to a ladder. The outside of the ladder is a sugar-phosphate backbone and the rungs are made of paired nitrogenous bases. These bases come in four varieties: Adenine (A), Thiamine (T), Cytosine (C), and Guanine (G). A always pairs with T and C always pairs with G along the rungs of the ladder.
The type of testing performed by Ancestry.com DNA is limited to areas of DNA that have the greatest application to genealogy which reveal insight into family relatedness. Heritage markers are within the non-coding regions and do not provide distinguishing information about an individual such as hair color. Typically there are three main kinds of analysis performed for genealogical purposes: DNA sequencing, Single Nucleotide Polymorphism testing (SNPs), and Short Tandem Repeat testing (STRs).
DNA Sequencing is the process of determining the exact base pair sequence in a predetermined section of DNA. This technique is most often used in mitochondrial DNA (mtDNA) testing where the sequence of hypervariable region I (HVR I) and hypervariable region II (HVR II) is determined. This kind of analysis is useful for direct maternal lineage testing or for maternal ancient ancestry typing.
Single Nucleotide Polymorphisms (SNPs, pronounced "snips") are single base pair changes that occur infrequently throughout the genome. SNP testing is available for mtDNA, and Y-chromosome. This testing can confirm an individual's deep ancestral grouping or haplogroup. While not directly genealogically (recent past) relevant, haplogroups are instead anthropological (ancient past) in nature. This type of analysis allows us to track the branching of haplogroups and subgroups from our original African home and discover interesting facts about our own ancient ancestor's movements across time and geography.
Short Tandem Repeats (STRs) are segments of DNA that repeat themselves, for example a GATA sequence repeated several times (GATA GATA GATA). Every individual has STR segments at specific locations on the chromosome. The specific locations are referred to as Loci or Markers and are generally noted as DYS###, for example DYS459. DYS indicates the location is on the Y-chromosome at position 459.
While everyone has these repeated regions, the distinction between one individual and another is the number of times the segment repeats. For example, at a given locus or marker on the chromosome, one individual may have 12 GATA's, and another individual may have only 10 GATA's. These numbers, 12 and 10, are called alleles. It is the collection of alleles for an individual at specific locations (loci) that make up his or her unique DNA profile or haplotype. These profiles or haplotypes are used for identification purposes, to determine paternity, or to establish relatedness.

Ancient Ancestry - Haplogroups

About Haplogroups
Humans began to diversify as they migrated out of Africa and populated the rest of the world, adapting to new climates, diets, and living conditions. Over tens of thousands of years, these ancient populations became isolated and their DNA changed until they became genetically distinct from one another. These deep ancestral groupings are referred to today as haplogroups. Through DNA testing, we can track the branching of haplogroups and their subgroups from the original African home and thus discover interesting facts about our own ancient ancestors' movements across time and geography. Ancestry.com DNA provides a complimentary haplogroup prediction with each Y-chromosome or mtDNA test.
Paternal Ancient Ancestry
Your Y-chromosome haplogroup can provide an interesting glimpse into the deep ancestry of your paternal line. Every race of people indigenous to this earth is a member of a particular haplogroup. Your Paternal Ancient Ancestry (or Haplogroup) is predicted based on your Y-DNA results. You will receive the name of the haplogroup, a detailed description of the group, and a map showing how your ancient ancestors migrated out of Africa over 100,000 years ago and split off to populate the different regions of the world.
Approximately 18 major paternal line haplogroups exist, known as A through R and are subdivided into subclades represented by numbers and subsequent subclades labeled with a lower case alphabetic character, e.g. E, E3, E3a. Haplogroup R1b is the most common haplogroup in European populations. It is believed to have expanded throughout Europe 10-12 thousand years ago.
Major Y-chromosome Haplogroups include:
  • R1b
  • I
  • B
  • E3a
  • E3b
  • J
Maternal Ancient Ancestry
Maternal ancient lineages or haplogroups can be subdivided into sub-lineages which are often regionally or population specific. For example, haplogroup H accounts for about 50% of European populations. It is believed to have originated in the Near East approximately 23,000-28,000 years ago and expanded into Europe about 20,000 years ago. Ancestry.com DNA examines multiple regions of the mitochondrial DNA to provide the most information possible about a maternal lineage. Participants can be either male or female.

Marker Listing

Y-DNA markers tested by Ancestry.com DNA
Marker Y-33 Y-46
*Y-GATA-H4 follows the TAGA motif as presented by Butler et. al. Forensic Sci. Intl. 129: 10-24.
DYS389 I
mtDNA regions tested by Ancestry.com DNA
Maternal Lineage Test(mtDNA)
HVR I - 16000 - 16569
HVR II - 1 - 390