Glossary of commonly used terms

Glossary

Here are some concise explanations for common terms in the world of DNA testing and genetic genealogy, along with links for further reading.

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Terms used on this site

Match
This refers to a person with whom you share enough DNA for them to be included in the list of matches provided by your DNA testing company (and/or Gedmatch). You can enter the match's name and/or kit number when you add segments to your profile.
Segment
A segment is a sequence within a chromosome that you share with a DNA match (for example: from 54,998,250-70,603,433 on chromosome 8). See below for a more detailed explanation.
Ancestor
An ancestor refers to a grandparent (or great grandparent, or more distant grandparent). DNA Painter helps you to use your match data to narrow down the ancestor who is the source of each match segment.
Group
This refers to a group of segments painted onto a DNA profile. As an alternative to assigning segments to an ancestor, you can group segments in other ways that might be useful:
  • You could collect significant yet unknown matches together in one place until you discover more.
  • You could collect matches together where you've identified but not proven the approximate ancestor whose family they originate from.
  • You might collect all segments from a group of matches in a group with a descriptive name (e.g. a place name or a hunch), and explanatory notes on your research to date.
Profile
A profile is a set of painted chromosomes for one person. You can create multiple profiles once you've registered a free account.

Terms used in Genetic Geneaology

Autosomal DNA Test
An autosomal DNA test provides information from your autosomes as well as your X-chromosome(s). Most commercial autosomal DNA tests give information about around 1 million genetic markers. This information can then be compared with others who have tested, and can be used to find people who are related to you. Current vendors of autosomal DNA tests include Family Tree DNA, Ancestry, My Heritage and 23andme.
Autosomal transfer
An autosomal transfer is when you test with one company but upload the data to another so that you can get matches from an extra database, as well as an additional ethnicity estimate. At present, only a few companies accept autosomal transfers. These include familytreedna.com, gedmatch.com, myheritage.com and dna.land. Further companies are expected to offer this service in the near future. You may need to do an autosomal transfer in order to obtain segment data for your matches.
Base Pair
A base pair is a building block of DNA that is used to measure chromosome length.
cM (Centimorgans)
Centimorgans are units used to describe the size of a DNA match segment. The length of the longest individual segment match is significant, as are the number of matching segments. The number itself is calculated statistically based on the properties of the chromosome and the match's position. In general, the higher the shared centimorgans, the more closely you'll be related to the match.
Chromosome
A human cell normally has 23 pairs of chromosomes. 22 of these pairs are autosomes, while the 23rd are the sex chromosomes. Females have two X Chromosomes, while males have one X and one Y chromosome.
Chromosome Browser
A chromosome browser is a tool that allows you to see the precise matching segments for a DNA match. Companies who provide an on-site chromosome browser include Family Tree DNA and Gedmatch. Ancestry.com notably do not currently include a chromosome browser in their online product, and instead offer a feature called 'Shared Matches', which presents common matches without revealing the segments they match on. A chromosome browser can be a powerful tool for identifying how matches relate to each other. However, it's also important to triangulate any matches in order to verify your findings.
DNA
DNA (deoxyribonucleic acid) is hereditary material that is found in human cells.
DNA Match
When you do a DNA test, the company you've tested with may process your result algorithmically and provide you with a list of DNA matches. These are individuals who have also tested, and with whom you have a significant amount of DNA in common. All companies have different criteria for what they consider significant, and some do not offer matches at all.
Endogamous Population
A community or population in which there has historically been a high proportion of marrying within the community (whether or geographical or religious reasons), with the result that the genetic profile of those from this community is more closed than the general population. An example of this in practice: those with Ashkenazi Jewish ancestry tend to share more segments than would be expected for their relationships, due to endogamy.
Gedmatch
A popular site that lets you upload your raw DNA into a database and then processes the data to locate matches. Gedmatch allocates a 'kit number' for each set of uploaded data. They provide a number of powerful tools, including 'People who match one or both of 2 kits', which is very helpful for triangulation.
Genealogical Timeframe
The genealogical timeframe refers to the period of time in recent history for which there are records that make it possible for us to trace our ancestors.
Genetic Recombination

While we all inherit 50% of our genes (23 chromosomes) from each parent, this is a random process; we don't inherit an equal number of genes from each ancestor (and going back in time, we may inherit none at all).

For example, while the 50% of our genes that we inherited from our father will have come from both of our paternal grandparents, the precise proportion passed on from each is random. This explains why we may be related to different extents to each of our grandparents, and why the number of shared centimorgans we have with more distant relatives and cousins varies so much.

IBD, IBS, IBC & IBP
These are all terms used to describe segment matches:
  • Identical by Descent (IBD) refers to a segment that you share with someone from a common ancestor within the geneaological timeline.
  • Identical by State (IBS) is used to describe a variety of scenarios where the segment cannot be tracked to a common ancestor, including IBC and IBP.
  • Identical by Chance (IBC) describes a segment where an accident of recombination means that a segment matches, but this is not a genuine match.
  • Identical by Population (IBP) refers to segments that are widely shared among populations, to the extent that they are not genealogically useful - e.g. in endogomous populations.
Inferred Match
A inferred match is where the source of an ancestral segment is deduced by elimination. For example:
  • You inherit half of your DNA (one of each autosome pair) from your mother.
  • This will be a mixture of DNA your mother got from her paternal and maternal side.
  • Say you discover a match for your mother via her paternal grandfather, but that you don't match with this person.
  • In this case, you can deduce that for these segments, you inherited DNA from your mother's mother, not her father.
Via this inferred match, you have then been able to paint some additional segments of your DNA.
Longest Segment
Within a match, the longest segment is significant. This is particularly important in endogomous populations. For example, if you are part Jewish and have a match with whom you share 84 cM in total, this might imply a third cousin match. However, if the longest segment is only around 10cM, these cM probably consist of many indentical-by-population (IBP) segments. By contrast, if the longest segment is at least 20cM, the match is far more likely to be traceable.
MRCA
The most recent common ancestor unsurprisingly refers to the closest common relative you have with a match. If a match is your full third cousin, then the MRCAs will be a set of great great grandparents.
mtDNA
This is DNA found in the mitochondria. mtDNA is inherited by males and females from their mother. An mtDNA test will provide a 'motherline' in the form of a named haplogroup. This can potentially be used to narrow down matches, but since mtDNA mutates very slowly, it's possible that those with whom you share mtDNA are only very distantly related to you. DNA Painter does not use mtDNA at this time.
Predicted relationship / Relationship Range / DNA Relatives
These are terms used by testing companies to explain their estimate of how close a connection you have to each DNA match based on the centimorgans and number of segments shared. Ancestry has a 'Predicted Relationship,' while Family Tree DNA has a 'Relationship Range' and 23andMe have the DNA Relatives feature. These are estimates and should be treated as a rough guide only.
Segment
A segment refers to a 'chunk' of a chromosome:
  • A shared segment with a DNA match is a consecutive series of base pairs on a chromosome for which there's at least half-match. Essentially, it's a chunk of one side of your chromosome pairs for which a match with someone else has been identified.
  • With each generation, DNA randomly recombines, leaving segments intact that were inherited from specific ancestors.
The aim of this site is to help people use shared segments to identify ancestral segments.
SNPs
Pronounced 'snips'; a single nucleotide polymorphism (SNP) is a type of genetic variation. You will see the number of SNPs shared in your match data alongside centimorgans. In scientific research, specific SNPs have been identified whose values can indicate particular health and characteristic information.
Triangulation
This is the process of verifying a DNA match via segment matches with three or more people, testing that matches match each other as well as the original tester, and then identifying a common ancestor via traditional genealogy for all of these people.
X-DNA
The X chromosome is passed to both males and females, but only via their mother. This makes X-DNA very useful for narrowing down the source of matches. An example:
  • You share 15.2cM of DNA on the X-chromosome with your mother's paternal cousin Peter.
  • Peter got all his X-DNA from his mother, who was your grandfather's sister.
  • You not only know that this shared X-DNA is from your grandfather; thanks to the inheritance pattern for X-DNA, you can also be certain that these segments came from your grandfather's mother, since he did not inherit any X-DNA from his father.
  • Thus from one match, you have been able to paint a match that you can attribute unambiguously to your mother's grandmother.
It's worth bearing in mind that FamilyTreeDNA take even tiny X-DNA matches and mark a match as 'X'. This is generally not accurate as matches of below 7cM are often chance matches as opposed to genuine ones.
Y-DNA
The Y chromosome is passed exclusively down the male line. Y-DNA tests are separate from autosomal tests, and can be very useful in some cases - e.g. where the father is not known. This site does not currently provide any visualisation tools for Y-DNA.