A Genetic Genealogy Glossary

This glossary is a work in progress.  Feel free to suggest additions or corrections. 

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admixture — interbreeding between two populations that had previously been separate; in genetic genealogy, the term is often used to mean the percentages of a genome that can be assigned to given populations

aDNA — abbreviation for ancient DNA

allele — a variant form of a gene; for example, the alleles I^A, I^B, and i are all variants of the gene for ABO blood type

Ancestry.com — a genealogy company that hosts family trees and offers subscription access to genealogical records (also called Ancestry)

Ancestry Composition — name for the admixture report at 23andMe

AncestryDNA — a genetic genealogy testing company that offers autosomal DNA tests with ethnicity estimates and relative matching

ancient DNA — DNA that has been recovered from ancient samples (abbreviated aDNA)

atDNA — abbreviation for autosomal DNA

autosomal DNA — DNA on a chromosome other than a sex chromosome; humans normally have 22 pairs of autosomal chromosomes (abbreviated atDNA)

avuncular — referring to the relationship between an aunt/uncle and their niece/nephew; see also nibling


base pair — a unit of DNA made of two nucleotides joined by weak chemical bonds; adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G) (abbreviated bp)

Bayesian analysis — a statistical method that allows an estimated of probability to be improved as more data become available; in phylogenetics, Bayesian analysis is sometimes used as shorthand for maximum-likelihood-based Markov-chain Monte Carlo methods

BigY — trade name for a yDNA test offered by Family Tree DNA that uses next-generation technology to sequence approximately 12 million base pairs of the Y chromosome; used to examine “deep” ancestral relationships and to identify new haplogroup-defining SNPs

birth parent (also birth mother, birth father)— a biological parent; used to distinguish a biological parent from a cultural parent when the two are not the same (e.g., in adoption, unknown parentage, or misattributed parentage)

bp — abbreviation for base pair; see also Mbp and kbp



centimorgan — a measure of genetic linkage between two positions along a chromosome; a segment of DNA that is 100 cM long will undergo an average of one crossing over event per generation (abbreviated cM)

centromere — the region of a chromosome where the two duplicated copies attach to one another during cell division; autosomal DNA tests for genealogy do not test SNPs in the centromere region, but crossing over there is rare, so a segment that seems to span the centromere can be safely considered a single, continuous segment

chromosome — an organizational unit of DNA; normal humans have 22 pairs of autosomal chromosomes and one pair of sex chromosomes (the word literally means colored body, based on how they look under a microscope when stained)

chromosome browser — a visual tool that displays the physical locations of matching DNA segments overlaid on a cartoon of the DNA tester’s own autosomal and/or X chromosomes; used for autosomal DNA test results

cM — abbreviation for centimorgan

common ancestor — when comparing two (or more) relatives, the shared ancestor to both of them; two relatives may have more than one common ancestor

cousin bait — a public display of information designed to find genetic cousins and encourage them to communicate (see cousin fishing)

cousin fishing — the process finding genetic cousins and encouraging them to communicate; the term cousin fishing is used loosely to describe methods such as autosomal DNA testing, posting a public family tree, blogging, etc.

crossing over — the exchange of DNA between paired copies of a chromosome during the first cell division of meiosis; crossing over causes shared segments to decrease in size over generational time



DD — abbreviation for DNA Detectives; as part of a user name, DD that person that the tester is either searching for biological family or willing to help someone searching

deletion — a type of DNA mutation caused by the deletion of one or more nucleotides

deoxyribonucleic acid — the chemical that transmit genetic information from one generation to the next (abbreviated DNA)

DNA — abbreviation for deoxyribonucleic acid; DNA is the chemical that transmits genetic information from one generation to the next

DNA Circles — trade name for a tool at AncestryDNA that identifies groups of DNA testers who are probably descended from a specific ancestor

DNA Day — commemorates the day (April 25, 1953) when the paper describing the structure of DNA was published; DNA testing companies may discount prices around this time

DNA Detectives — may refer to the media consulting company run by CeCe Moore or its offshoot Facebook support group for individuals using DNA test results to seek biological family

DNA Relatives — trade name for the relative matching tool at 23andMe

DNAgedcom — a website with tools to assist with genetic genealogy analyses

DNALand — a website with tools to assist with genetic genealogy analyses and to contribute to biomedical research

downstream — the portion of a haplogroup tree descended from the node where a given SNP first appears



endogamy — the practice of finding mates within the same group, such as a religious, ethnic, or geographic group; endogamy can cause relatives to share more DNA than expected given the relationship

Ethnicity Estimate — name for the admixture report at AncestryDNA


evolution — a change in allele frequencies in a population over generational time

Exploring Family Trees — a website with tools for visualizing family trees



false match — see false positive

false positive — a DNA segment that seems to match between two people but that was not inherited from a parent; false positives are statistical anomalies resulting from the fact that microarray DNA tests cannot assign alleles to one paren to the other

Family Finder — trade name for the autosomal DNA test offered by Family Tree DNA

FamilySearch — a genealogy organization that hosts family trees and offers free access to genealogical records

Family Tree DNA — a genetic genealogy testing company that offers autosomal, mitochondrial, and yDNA tests (abbreviated FTDNA); their autosomal test includes a ethnicity estimates, and all of their tests match you to DNA relatives

FIR — abbreviation for fully identical region

fishing — see cousin fishing

FTDNA — an abbreviation for the company Family Tree DNA

fully identical region — a segment of DNA in which two people share identical SNPs on both copies of that chromosome, meaning they each inherited that segment from both parents  (abbrevaited FIR)



gamete — a sex cell (egg or sperm)

g.d. or gd — abbreviation for genetic distance

GEDmatch — a website with tools to assist with genetic genealogy analyses

gen — at GEDmatch, a number representing the typical number of generations separating two DNA matches sharing a given amount of DNA; for example, a gen of 2 implies that the common ancestor is two generations back at the grandparent level

gene — a unit of DNA that influences an individual’s characteristics; the various forms of a given gene are called alleles; for example, the ABO gene for blood type has three alleles, I^A, I^B, and i

Genetic Communities — trade name for a tool at AncestryDNA that can assign DNA testers to groups based on their genetic connections within each group

genetic distance — a whole number that indicates the number of mutations that differ between two people who have taken the same yDNA or mtDNA test; a genetic distance of zero means an exact match (abbreviated g.d. or gd)

genetic genealogy — a discipline in which DNA tests results are used to assist genealogy research

genetics — the field of biology that studies genetic inheritance, mutation, gene expression, and genetic variation; see also population genetics

genome — all of the genetic material in a species, individual, or organelle (e.g., human genome, nuclear genome, mitochondrial genome)

Genome Mate Pro — a software program for managing DNA test results



half identical region — a segment of DNA in which two people share identical SNPs on one of two copies of that chromosome, meaning they each inherited that segment from one parent (abbrevaited HIR)

haplogroup — a group of haplotypes that are related by common descent and usually defined by a SNP mutation

haplotree — a visual depiction of the phylogenetic (evolutionary) relationships among haplogroups

haplotype — the sequence of a DNA segment that is inherited intact from a single parent; most commonly used for Y chromosome DNA and mitochondrial DNA

HIR — abbreviaiton for half identical region



IBC — abbreviation for identical-by-chance or identity-by-chance

IBD — abbreviation for identical-by-descent or identity-by-descent

IBS — abbreviation for identical-by-state or identity-by-state

ICW — an abbreviation for in common with

identical-by-chance (also identity-by-chance) — a term to describe DNA segments that are identical or nearly identical because of chance events rather than common ancestry (abbreviated IBC)

identical-by-descent (also identity-by-descent) — a term to describe DNA segments that are identical or nearly identical because they were inherited from a common ancestor (abbreviated IBD)

identical-by-state (also identity-by-state) — a term to describe DNA segments that are identical or nearly identical; although technically the term does not imply why the segments are identical, it is commonly used to mean identical-by-chance (abbreviated IBS)

in common with (also relatives in common, shared matches) — a term to describe DNA matches to a tester who also share DNA with one another (abbreviated ICW)

indel — a type of DNA mutation caused by the insertion or deletion of one or more nucleotides; the term is formed by combining the words insertion and deletion

independent assortment — the biological principle that alleles for one gene will be passed on to a child independently of alleles for a different gene; independent assortment causes segments to be passed on randomly to the next generation

informed consent — permission given for an act by someone who has legal authority and who clearly understands the facts, implications, and consequences of the action; in genetic genealogy, informed consent is needed from the tester or a legal representative to participate in scientific research projects

insertion — a type of DNA mutation caused by the insertion of one or more nucleotides

International Society of Genetic Genealogy — an organization that advocates for and educates about genetic genealogy

ISOGG — abbreviation for International Society of Genetic Genealogy; the abbreviation is sometimes used to refer to the society’s Facebook group or its wiki




kbp — abbreviation for kilo base pairs, or 1,000 base pairs of DNA


likelihood — see maximum likelihood

Living DNA — a DNA testing company whose product includes ethnicity estimates, haplogroup assignments, and a biogeographical analysis; as of April 2017, it did not offer relative matching


maximum likelihood (also likelihood) — an advanced method for estimating phylogenetic trees that incorporates some of the known complexities of DNA mutation and evolution (abbreviated ML)

maximum parsimony (also parsimony) — a basic method for estimating phylogenetic trees that uses simplified assumptions about how DNA mutates and evolves (abbreviated MP)

Mbp — abbreviation for mega base pairs, or 1,000,000 base pairs of DNA

MDKA — abbreviation for most distant known ancestor

meiosis (plural meioses) — a type of cell division that produces gametes (eggs or sperm); during meiosis, the amount of DNA present in normal body cells is halved

microsatellite — see short tandem repeat

microsatellite mutation — a type of mutation in which a repeating string of nucleotides (called a microsatellite or short tandem repeat) increases or decreases in length

migration — the movement of individuals, groups, or populations from one geographic region to another; this use of the word should not be confused with seasonal movements of some animal species, such as birds

mirroring — a technique used at AncestryDNA to identify where in a DNA match’s tree the probable common ancestor is

misattributed parentage event — (also non-parental event) — a situation in which a presumed parent is not the biological parent (abbreviated MPE)

mitochondrial DNA — DNA found in the mitochondrion; it is made up of about 16,569 base pairs arranged in a circle (abbreviated mtDNA)

mitochondrion (plural mitochondria) — an organelle in body cells that produces energy; it has its own DNA separate from the nuclear DNA

mitosis — a type of cell division that normally results in two daughter cells with the same genetic makeup; most body cells divide this way

ML — abbreviation for maximum likelihood

MP — abbreviation for maximum parsimony

MPE — abbreviation for misattributed parentage event

MRCA — abbreviation for most recent common ancestor

mtDNA — an abbreviation for mitochondrial DNA

mutation — a change in the nucleotide sequence; mutations of most interest to genetic genealogy are point mutations, indels, and microsatellite mutations

MyHeritage — a genealogy company that hosts family trees, offers subscription access to genealogical records, and provides autosomal DNA tests

myOrigins — trade name for the admixture report at Family Tree DNA



NAD — abbreviation for New Ancestor DiscoveriesNAD is often used in the singular to refer to the relative suggested by the tool

New Ancestor Discoveries — trade name for a feature offered by AncestryDNA that suggest possible ancestors or relatives who are not already in the tree linked to a given DNA test result (abbreviated NAD)

nibling — a niece or nephew; sometimes used to refer generally to the aunt/uncle–niece/nephew; see also avuncular

non-paternity event (also non-parental event, misattributed parentage event) — a situation in which a presumed father is not the biological father; less commonly, the term can be used for a misattributed mother, for example in the case of adoption or a step-mother (abbreviated NPE)

NPE — abbreviation for non-paternity event or non-parental event

nuclear DNA — DNA found in the nucleus of the cell; nuclear DNA includes the autosomes and the sex chromosomes and represents the vast majority of the human genome

nucleotide —a chemical building block of DNA; the four nucleotides are commonly referred to by their key subunits: adenine (A), cytosine (C), guanine (G), and thymine (T)



organelle — a compartment within a cell that has a specific function; the two organelles relevant to genetic genealogy are the nucleus (where nuclear DNA is found) and the mitochondrion (where mitochondrial DNA is found)



PAR — abbreviation for pseudoautosomal region of the X and Y chromosomes

parsimony — see maximum parsimony

phasing — the process of determining which autosomal SNP alleles are associated with other SNP alleles on the same maternal or paternal chromosome; see also trio phasing and statistical phasing

phylogeny (also phylogenetic tree) — a branching diagram that shows the inferred evolutionary relationships among taxonomic units; the taxonomic units can be species, populations, haplogroups, languages, or other any other entity that has an evolutionary relationship to others

pile-up — a layperson term for excess IBD

point mutation — a type of mutation in which one nucleotide is replaced by another

population genetics — a subfield of genetics that concerns genetic variation within and among populations, usually in the context of evolution; see also genetics

private tree — a family tree that is not accessible to others without express permission from the tree’s owner

pruning — a method used with AncestryDNA results to identify a shared ancestor in a private tree

pseudoautosomal region — a region of DNA where the X and Y chromosomes recombine; the pseudoautosomal region on the short arm of chromosomes X and Y (PAR1) is 2.6 Mbp, and the one on the long arms (PAR2) is 320 kbp (abbreviated PAR)

public tree — a family tree that can been viewed by others without express permission from the tree’s owner

purine — a chemical class that includes the nucleotides A and G

pyrimidine — a chemical class that includes the nucleotides C and T



qualitative trait — a genetic trait that is controlled by one or two genes that can take on only a few discrete values, e.g., ABO blood types

quantitative trait — a genetic trait that is controlled by multiple genes and that can take on a range of values, e.g., height



raw data — the results of a laboratory DNA test; the raw data include only the base calls or STR results for the person tested

recombination — the exchange of genetic material between homologous chromosomes during meiosis; crossing over (Note: there are other forms of recombination not included in this definition, but they are not generally relevant to genetic genealogy)

recombine — to undergo recombination

relatives in common (also in common with, shared matches) — a term to describe DNA matches to a tester who also share DNA with one another

remove — a term used to describe a generational difference between cousins; once removed refers to one generational difference, twice removed to two, etc.; for example, first cousin once removed describes the relationship between a person and the child of his/her first cousin

ROH — abbreviation for run of homozygosity

run of homozygosity — a segment of a paired chromosome that is identical on both copies of that chromosome, meaning it was inherited from both parents (abbreviated ROH)



search angel — an experienced volunteer who helps others find biological family, usually in cases of adoption or other unknown parentage

segment — a length of DNA that was inherited intact from an ancestor

sex chromosome — a chromosome that determines biological sex; a person normally has either two copies of the X chromosome and is female or has one X and one Y chromosome and is male

Shared Ancestor Hint — trade name for a tool at AncestryDNA that identifies common ancestors in the trees of a tester and their DNA matches

Shared cM Project — a crowd-source project that compiles real-world data on the ranges of shared DNA amounts for known relationships

shared matches (also in common with, relatives in common) — a term to describe DNA matches to a tester who also share DNA with one another

short tandem repeat (also microsatellite) — a string of 2–5 base pairs that repeat in a DNA sequence, e.g., ATCATCATCATCATC; the number of repeats in an STR can reflect family history; commonly used for yDNA

single-nucleotide polymorphism — a nucleotide position in the genome that is known to vary among individuals because of point mutations (abbreviated SNP)

SNP — abbreviation for single-nucleotide polymorphism (pronounced “snip”)

statistical phasing — a method of phasing autosomal DNA results using haplotype frequencies from a reference population rather than parent–child trios; see also phasing and trio phasing

STR — abbreviation for short tandem repeat



taxonomic unit — an entity represented in a phylogenetic tree

terms of service (also terms of use) — the legal agreement between a customer and a company, in this case a DNA test taker and the DNA testing service

Timber — trade name for a computer algorithm used by AncestryDNA to reduce the effects of excess IBD (pile-ups) on DNA matching

time to most recent common ancestor — an estimate of the number of years ago the most recent common ancestor of two or more people lived; usually based on an estimated mutation rate and average age of reproduction (abbreviated tMRCA or TMRCA)

TMRCA (also tMRCA) — abbreviation for time to most recent common ancestor

transition — a point mutation between two nucleotides that belong to the same chemical class, i.e., between A and G (both purines) or between C and T (both pyrimidines); see also transversion

transversion — a point mutation between two nucleotides that belong to different chemical classes, i.e., between a purine (A or G) and a pyrimidine ((C or T); see also transition

triangulation — a technique in which three or more people who all share the same segment of DNA compare family trees to infer which common ancestor contributed that segment

triangulation group — a group of three or more people who all share the same segment of DNA (abbreviated TG)

trio phasing — a method of phasing autosomal DNA results using data from a child and both parents



upstream — the portion of a haplogroup tree ancestral to the node where a given SNP first appears




white paper — a  report, usually produced by one of the DNA testing companies, describing the scientific details of a feature or service



X chromosome — a sex-determining chromosome present in all individuals; normally, women have two copies of the X chromosome and men have one copy of the X chromosome and one of the Y chromosome



Y chromosome — a sex-determining chromosome present normally only in men

yDNA — DNA on the Y chromosome





23andMe — a genetic testing company that offers an autosomal DNA test that includes haplogroup assignment and ethnicity estimates, with optional health reports and relative matching


Still To Be Defined


Evil Twin

excess IBD

haplotype —



homozygosity —


institutional review board — (abbreviated IRB)


linkage disequilibrium

most distant known ancestor — (abbreviated MDKA)

most recent common ancestor — (abbreviated MRCA)


next generation sequencing — (abbreviated NGS or next-gen)



reference panel




Ethiohelix —

Eurogenes —

GedrosiaDNA —

HarappaWorld —

MDLP Project —

PuntDNAL —



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