FAQ / Terminology
As you learn more about DNA, there may be terminology that is unfamiliar to you, and you may have a few questions. Learn more about unfamiliar terminology, and get answers to common questions below.
Frequently Asked Questions
DNA, or deoxyribonucleic acid, is the genetic code that defines each person’s biological characteristics. DNA is chains of four 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 two 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, four types of DNA are used to discover more about your ancestry:
Autosomal DNA includes all 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.
The Y chromosome (one of the two paired sex chromosomes) is only carried by men and is passed from father to son. By comparing the Y chromosome of two males, you can determine whether they share a common patrilineal ancestor.
The X chromosome (one of the two 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 to her son or daughter. By comparing the X chromosome of two individuals, you may identify a common ancestor if that segment comes from an ancestor in your direct X path.
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 two 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 five to seven generations. Beyond five to seven 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 second cousin or closer.
Yes, DNA can be used to solve family history problems. However, testing your DNA is just one 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, etc. 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:
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 member, please secure proper permissions from them and educate them on the potential impact of posting their DNA data on any website. For guidance in using your DNA, or the DNA of others, as part of your research, please review the Genetic Genealogy Standards at www.geneticgenealogystandards.com.
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. 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. Requires registration. (https://www.dnagedcom.com)
DNA Painter—DNA Painter provides a user-friendly online tool for chromosome mapping. (https://dnapainter.com)
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 using DNA as part of your 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.
Admixture: See Ethnic Origins
Autosomes: The 22 nonsex chromosomes within the nucleus of a cell
atDNA (autosomal DNA): One type of DNA used in genetic genealogy that utilizes the 22 nonsex chromosomes
Base Pair: Two complementary bases located on opposing DNA strands; see nucleotide
Centimorgan (cM): A unit of measurement for DNA segments. Generally, the more cMs shared between individuals, the more genetically “related” they are. A DNA shared cMs chart can be very helpful in identifying possible family relationships, based on the number of cMs of each individual.
Chromosome: A strand of DNA within the nucleus of a cell that carries genetic information
Chromosome Browser: A feature offered by some genealogy companies that allows you to view matching segments on a visual map of the chromosomes
Chromosome Mapping: The process of assigning ancestors to individual DNA segments
DNA (deoxyribonucleic acid): The genetic code that defines each individual’s biological characteristics
DNA Project: A group of people whose DNA or surname indicates a biological connection; project administrators for DNA projects are knowledgeable and group the DNA results of group members
Endogamy: The practice of limiting marriage to members of one’s specific social group (such as tribe, community, ethnic group); using DNA within an endogamous group becomes more difficult
Ethnicity estimates: Approximate amounts of DNA inherited from various ethnicities based on a comparison between your DNA and reference samples; DNA testing companies report ethnicity estimates differently
Genetic Genealogy: The use of DNA test results to establish or confirm genealogical relationships
Genetic Genealogy Standards: Ethical and usage standards in using DNA established as guidelines for genealogists and others. See http://www.geneticgenealogystandards.com/
Haplogroup: Group of similar haplotypes that share a common ancestor identified by a single, well known mutation
Haplogroup Project: A project consisting of those who share a common haplogroup
Haplotype: A group of alleles that are inherited together, also known as a genetic signature
IBD (identical by descent): A segment of DNA that is found to be identical (except for rare mutations or testing errors) in two people who are related to each other due to the fact that this segment was passed down to both of them from a common ancestor.
IBS (identical by state): A region of the genome where two people share at least one matching allele for every allele reported (allowing for possible mutations or testing errors)
ISOGG Wiki: A reference wiki built and maintained by the International Society of Genetic Genealogists; see https://isogg.org/wiki
Match: Individual identified by a DNA company as having shared segments of DNA
Mitochondria: Located in the cytoplasm of a cell, the mitochondria are the cell’s powerhouses
MRCA (most recent common ancestor): The most recent ancestor (or ancestral couple) that is shared by two individuals
mtDNA (mitochondrial DNA): DNA associated with a cell’s mitochondria, passed down from mother to child
Mutation: A change in a person’s DNA
NPE (non-paternal event): When the parent identified through paper trail research is not the biological parent
Nuclear DNA: DNA located in the cell’s nucleus; These include the 22 paired autosomes and the sex chromosomes, making 23 pairs in all
Nucleotide: The basic building blocks of the DNA molecule; The 4 known nucleotides are adenine (A), guanine (G), cytosine (C), and thymine (T)
Paper Trail: Genealogy done by researching traditional records such as census, probate, vital, etc.
Phasing: The process of discovering which allele data was contributed by each parent
Surname Project: A project researching the genealogical origins of persons with a given surname
Tree Triangulation: The process of proving a genealogical relationship by showing that 3 (or more) individuals independently share a paper trail and inherited DNA from a common ancestor
xDNA: One of the 2 sex chromosomes; individuals with 2 X chromosomes are female; x chromosomes have a unique inheritance pattern because an X chromosome cannot be passed from father to son