Genetic Genealogy FAQ

DNA, or deoxyribonucleic acid, is the genetic code that defines each person’s biological characteristics. DNA is chains of 4 individual nucleotide links, the sequence of which encode our genetic information. These strings of DNA are coiled into packages called chromosomes. Chromosomes are found in the cell nucleus. Each nucleus contains 23 paired chromosomes. One of these pairs (the sex chromosomes) is composed of 2 X chromosomes for females or an X and a Y chromosome for males. The other 22 paired chromosomes are known as autosomes.

Cells also have mitochondria outside the cell’s nucleus. Mitochondria have their own DNA.

DNA can provide information in different ways to help you identify your related family members and ancestors, depending on which part of the DNA molecule is used. Typically, 4 types of DNA are used to discover more about your ancestry:

atDNA
Autosomal DNA includes all of the chromosomes (excluding the sex chromosomes). Autosomal DNA can help identify ancestors within the last 5–7 generations. However, because you only inherit half of each of your parents’ DNA, some of your ancestors “fall off” your genetic tree (meaning you did not inherit any of their DNA). You are also guaranteed to only share DNA with 2nd cousins or closer.

yDNA
The Y chromosome (1 of the 2 paired sex chromosomes) is only carried by men and is passed from father to son. By comparing the Y chromosome of 2 males, you can determine whether they share a common patrilineal ancestor.

xDNA
The X chromosome (1 of the 2 paired sex chromosomes) is carried by both males and females (females as “XX,” males as “XY”) but can only be passed down from a mother (not the father) to her son or daughter. By comparing the X chromosome of 2 individuals, you may identify a common ancestor if that segment comes from an ancestor in your direct X path.

mtDNA
MtDNA, or mitochondrial DNA, is found in a cell's mitochondria. Mitochondria are passed from a woman to all her children, regardless of whether they are male or female. By comparing the mitochondrial DNA of 2 individuals, you can determine whether they share a common matrilineal ancestor.

Haplogroup designations may be included in your test results for YDNA (father line) and mtDNA (mother line). Haplogroups are groupings of DNA similarities that reflect ancient migration patterns before genealogical records were created. YDNA haplogroups match with modern usage of surnames and can be helpful in solving problems on your surname line. mtDNA haplogroups reflect more variety and are loosely tied to your maternal ethnic origins.

Your family tree is what has been documented over time through family history records and often reflects relationships, some of which may not be biological. Your genetic tree consists of the relatives with whom you share DNA, which you mutually inherited from common ancestors within the last 5 to 7 generations. Beyond 5 to 7 generations, you may not share DNA with all your ancestors according to your family tree. Therefore, not all of your family tree ancestors will be revealed in your genetic tree from your DNA results.

DNA is inherited randomly, which means the DNA segments you inherited from your ancestors may be different than the DNA your relative inherited from the same ancestors. You are only guaranteed to share DNA with a 2nd cousin or closer.

Yes, DNA can be used to solve family history problems. However, testing your DNA is just 1 step in a larger process. You will likely need a combination of DNA and traditional research to identify family history connections.

DNA test results may reveal unexpected information about your family history, such as adoptions, unexpected paternity, and so. The affected party may be yourself or a close DNA relative—perhaps someone you know nothing about. If this new information may be upsetting to you or to another family member, you may want to prepare family members in advance of possible results, or perhaps test at a later date. If you are not prepared to learn unexpected information, a DNA test may not be right for you at this time. Multiple companies provide DNA testing, each offering different tests and resources to customers.

If you receive unexpected results, such as the identity of parents, grandparents, great-grandparents, or other previously unknown relatives, be sensitive and considerate of others involved who may be affected by the results. Approach family members with care and support as you discuss these previously unknown events.

Multiple community groups provide support and guidance on dealing with unexpected information:

NPE Gateway
DNA Secrets
Watershed DNA
Donor Conception Network
NPE Fellowship
ISOGG Unexpected Results wiki page

You may want to invite other family members to test their DNA. In some instances, you may need to oversee the testing and administration of their account on the DNA test service website. Before testing any family members, please secure proper permissions from them and educate them on the potential impact of posting their DNA data on any website.

Most DNA companies will allow you to download your raw DNA results to preserve and potentially share with other companies. You can upload this raw data to some DNA companies for additional cousin matching. You will need to get instructions on how to do this from the company you tested with.

Many tools and services are available to assist you in utilizing your DNA in a variety of ways. Below are a few possible tools, with many others available:

GEDMatch—GEDMatch lets you upload and compare your raw DNA data, regardless of which company you tested with. GEDMatch also provides additional admixture tools, one-to-many comparison, one-to-one comparisons, and more. Using this tool requires registration and contribution of a raw DNA file (https://gedmatch.com).

DNA Gedcom—Use the Autosomal DNA Segment Analyzer to group matches by segment using your 23andMe or FamilyTreeDNA data. DNA Gedcom also includes GWorks, a tool which compares GedCom files. Using this tool requires registration (https://www.dnagedcom.com).

DNA Painter—DNA Painter provides a user-friendly online tool for chromosome mapping. (https://dnapainter.com)

Autosomal DNA Tools List
Mitochondrial DNA Tools List
Y-DNA Tools List

Consider these resources in learning more about DNA and how you can use it effectively in your own family history activities:

ISOGG Wiki—The International Society of Genetic Genealogists has created and maintains a wiki (community written encyclopedia) on DNA and how it is used for genealogy (isogg.org/wiki).

Genetic Genealogy Standards—The genetic genealogy community has established a set of standards for genealogists who use DNA as part of their research (www.geneticgenealogystandards.com).

Autosomal DNA testing comparison chart—For a detailed chart of several top DNA testing companies, check this link found on the ISOGG (International Society of Genetic Genealogy) website (https://isogg.org/wiki/Autosomal_DNA_testing_comparison_chart).

DNA testing companies list—ISOGG provides a list of known DNA testing companies with a link to each website (https://isogg.org/wiki/List_of_DNA_testing_companies).

FamilySearch Blog—Blog page with DNA articles

When your DNA test results are posted on a company website, you should have the option to share your data with everyone, with selected individuals, or to keep it private. Caution: Be aware that any time your results are stored by an organization, even if you opt not to share data, there is no 100% guarantee that someone will not be able to identify or use your data in another way. For some people, this is not an issue. For others, it is an important concern.

When you test with any DNA testing service, you will be required to sign a consent form to allow that company to acquire, test, and store your DNA and analysis data and to provide certain services. That consent form may include an option in which you provide consent to let them use your DNA for medical research purposes, assuring you that your DNA data will be “anonymized,” which removes your identity from that data. You have the right to deny their use of your DNA results for medical research purposes, if you prefer. Law enforcement agencies may utilize a data aggregate company, if users have opted in to share their DNA test results. Most genetic genealogy companies do not share your DNA results with law enforcement unless court ordered. However, you should read the consent forms carefully for each company.

FamilyTree DNA and FamilySearch Family Tree are separate products owned by different organizations. FamilyTree DNA is a testing company owned by Gene by Gene. FamilySearch Family Tree is the world’s largest shared free family tree, found online on FamilySearch.org.