Glossary of Genetic Genealogy Terms

 International Society of Genetic Genealogy's

Used with ISOGG's permission
Many of these terms were created and provided by ISOGG, last updated 5/25/06.  Posted on our site 2/16/07, Updated 12/04/07

Genetic genealogy terms and definitions compiled and designed to be as simple and easy to understand as possible.  Additional and more technical definitions are available on several other glossary websites.  Terms and definitions are bookmarked to assist comprehension. 

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O P  Q  R  S  T  U  V  W  X  Y  Z


Administrator - Also known as a 'Project Administrator', 'Group Project Administrator', 'Project Manager', 'Coordinator' and 'Co-Coordinator'.  A volunteer who establishes a DNA study with one or multiple commercial DNA testing companies.

Admixture DNA - The non-gender chromosomes that mix or recombine. Also known as autosomal DNA.

Allele - (pronounced UH-leel) - The scientific result for a marker.

Ancestral haplotype - The method of deducing the MRCA's haplotype by comparing matching descendants' haplotypes, and eliminating the mutations.  A minimum of three lines, as distantly related as possible, is recommended for deducing the ancestral haplotype.

Ancestral state - Refers to the state of a SNP that has mutated and is shared by the most people.  Example:  A negative result on a SNP means it is ancestral, a positive result means it is derived.

Anthrogenealogy - A term coined by Family Tree DNA combining the words 'anthro' and 'genealogy' in reference to utilizing DNA to trace one's heritage far beyond recorded documentation. 

Atlantic Modal Haplotype (AMH)  See Western Atlantic Modal Haplotype

atDNA - Acronym for Autosomal DNA.

Autosomal DNA - The non-gender chromosomes that mix or recombine. Also known as admixture DNA.


Base - The unit or building block of DNA. Adenine (A), cytosine (C), guanine, (G), and thymine (T) are the four bases in DNA. The order of bases is the sequence of DNA.

Base pair - Two bases bonded together and attached to one of the strands in the DNA double helix. Adenine always pairs with thymine, and guanine always pairs with cytosine.

Buccal cell - A type of cell found in cheek tissue inside the mouth


Chromosome - A structure found in the nucleus of a cell that contains genetic material. Humans have 23 pairs of chromosomes; 22 pairs of autosomes and one pair of sex chromosomes.

Coding region - A region of DNA which contains genes.

Cohanim Modal Haplotype - The Y-DNA haplotype most commonly found among males with an oral tradition of Cohen ancestry.

Cohen - The Hebrew word for priest which refers to a direct male descendant of Aaron, the brother of Moses; plural: Cohanim.

Combined DNA Index System (CODIS) - The CODIS system uses marker locations in the autosomal DNA. CODIS test results are maintained in an FBI database which is used to identify people and solve crimes.

Complementary sequences - Opposing strands of DNA which bond together to form the double helix. The bases always complement one another with adenine and thymine pairing together and cytosine and guanine pairing together.

Convergence - The process of two unrelated or less related lineages changing over time to resemble one another.

Cross-over - See recombination.

CRS - Acronym for Cambridge Reference Sequence. The first mitochondrial DNA to be fully sequenced at Cambridge University in 1981.  The anonymous donor of the CRS was haplogroup 'H'.  Mitochondrial results are determined based upon where the results differ from the CRS.


Deoxyribonucleic acid (DNA) - A chemical consisting of a sequence of hundreds of millions of nucleotides found in the nuclei of cells. It contains the genetic information about an individual and is shaped like a double-stranded helix.

Derived state - Refers to the state of a SNP that has mutated, usually in one man, from the ancestral state and created a new haplogroup or sub-clade of a haplogroup.  A positive SNP result is derived, a negative SNP result is ancestral

DNA amplification - The production of many DNA copies from one or a few copies or fragments.

DNA replication - The process by which the DNA double helix makes a copy of itself or of a fragment of itself. It uses the old DNA as a template for the synthesis of new DNA strands. In humans, replication occurs in the cell nucleus.

DNA sequencing - The process of determining the exact order of the nucleotide bases in a segment of DNA.

DNA Y-chromosome Segment (DYS) - The "name" of a marker on the Y-chromosome. It is assigned based on a nomenclature system controlled by the HUGO Gene Nomenclature Committee, which assigns DYS numbers to newly discovered markers.

DNAF - Acronym for DNA-Fingerprint - a commercial DNA testing company.

DNAH - Acronym for DNA Heritage - a commercial DNA testing company.

DNA-NEWBIE - A DNA-Newbie is someone who is new to the field of genetic genealogy.  It is also the name of a Yahoo mailing list forum sponsored by the International Society of Genetic Genealogy.

Double helix - The twisted shape DNA forms when its two strands bond together. A double helix looks like a twisting or rotating ladder.DYS - Acronym for DNA Y-chromosome Segment - The assigned number of a marker on a segment of the Y-chromosome.  Example: DYS# 393


Enzyme - A protein that facilitates a specific chemical reaction by working as a catalyst.

Exact match - Two individuals with exactly the same results for all markers or regions compared.


FTDNA - Acronym for Family Tree DNA - a commercial DNA testing company.

Family Tree DNA Time Predictor (FTDNATiPTM) - A program used to calculate estimates of Time to the Most Recent Common Ancestor (TMRCA). It is the world's first calculator that incorporates mutation rates specific to each marker. This greatly increases the power and precision of estimates.


GAP - Acronym for the Group Administrator Page - This is a webpage in which a DNA Project Administrator utilizes functions such as creating a public website, generating a FTDNATiP report, etc. to assist project participants in coordinating results. 

GEDCOM - Acronym for Genealogical Data Communications - A plain text program created for exchanging genealogical data between different genealogical programs.  Family Tree DNA's 'My FTDNA' page, Y-Search and Mitosearch all contain a feature to upload a GEDCOM for pedigree comparisons to matches.

Gene - A segment of DNA which contains the genetic code to make a certain protein or part of a protein.

Generation - The number of years between the birth of the parents and the birth of their children. Different studies use different numbers of years per generation.  Family Tree DNA uses 25 years.

Genetic cousins - Individuals whose Y-DNA or mtDNA test results match one another.

Genetic distance - The number of differences, or mutations, between two sets of results. A genetic distance of zero means there are no differences in the results being compared against one another (exact match).

Genetic Genealogy - The latest tool for genealogists utilizing DNA to aid genealogical research.

Genetics - The study of genes and heredity; the study of DNA.

Genographic Project - (pronounced GENE-o-graphic) - A five-year scientific genetics project launched in 2005 to study and map human migratory patterns.  Along with testing indigenous populations, the project offers a 12-marker Y-chromosome or HVR1 mtDNA test for public participation with a portion of the proceeds benefiting the indigenous communities.  The project is sponsored by National Geographic, IBM and the Waitt Foundation.  Genographic participants have the option to join Family Tree DNA's database once their DNA results are in.

Genome -
The entire complement of genetic material in a chromosome set. The human genome is composed of 46 chromosomes, with a total of 3 billion base pairs.

Genotype - The genetic makeup of an individual organism.


Haplogroup - A group of similar haplotypes that share a common ancestor with a SNP mutation.  Because a haplogroup consists of similar haplotypes, this is what makes it possible to predict a haplogroup.  A SNP test confirms a haplogroup.  Haplogroups are assigned letters of the alphabet, and refinements consist of additional number and letter combinations, Example: R1b1. Y-chromosome and mitochondrial DNA haplogroups have different haplogroup designations.  Haplogroups pertain to your deep ancestral origins dating back thousands of years.  

Haplotype - The term for the set of numbers that consists of your Y-chromosome or mitochondrial DNA results.  Haplotypes are also known as signatures.

HVR - Acronym for Hyper Variable Region - The sections of non-coding mitochondrial DNA that are used for genealogical DNA testing.


ISOGG - Acronym for the International Society of Genetic Genealogy, a free society founded in 2005 for the promotion and education of genetic genealogy.


JoGG - The Journal of Genetic Genealogy - An online journal published quarterly with articles and features pertaining to genetic genealogy and anthrogenealogy.

Junk DNA - Slang term usually used in referring to the non-coding region of DNA on the Y-chromosome.  For more about:


Marker - A type of non-coding Y-chromosome DNA. The numbers designating your individual DNA segment numbers you receive with Y-chromosome DNA results. Example: 393=13.  This means at marker #393, your allele value is 13.

Meiosis - The stage in which sperm and egg cells are formed. It is during this process that the autosomal chromosomes recombine and mutations occur.

Microsatellite - See short tandem repeat.

Mitochondria - A specific organelle in the cell that helps it to produce energy.

Mitochondrial DNA - Energy releasing organelles located in the cytoplasm of cells, which contain their own DNA.  Mitochondrial DNA is passed from mother to child, but only females continue to pass on their maternal mitochondria to their children. 

Mitosearch - A free public database sponsored by Family Tree DNA where mitochondrial DNA results from any testing facility may be uploaded and compared.

Modal haplotype - The most common result for each marker tested in a group of results. See also: ancestral signature.

MRCA - Acronym for Most Recent Common Ancestor. 

mtDNA - Acronym for mitochondrial DNA.

Mutation - A change in the DNA that occurs at random.  Mutation is a scientific term that often connotes a negative connotation as a result of 1950's 'B' movies, but in genetic genealogy, a mutation is usually beneficial.  Mutations on the Y-chromosome are often used for distinguishing different ancestral lines.

Mutation rate - The frequency with which random mutations occur.


Non-coding DNA - Also referred to as "Junk DNA", non-coding DNA has no known biological function.

Nuclear DNA - DNA of chromosomes found in the nucleus of the cell.

Null - A null is a value of zero on a marker.  Nulls can occur due to missing genetic material on a marker, or a SNP can sometimes cause a null result.  Several YSTR markers have been identified in certain families to have null results: 439, 448


OA - Acronym for Oxford Ancestors - a commercial DNA testing company.

Organelle - A cell structure with specialized functions.


Pherogram - For STRs, a plot which shows the length of a fragment of DNA. This allows its allele value to be measured.

Phylo-tree - Shortened term for Phylogenetic Tree - Most often used in reference to the available online diagrams connecting all Y-chromosome haplogroups.  This term is also applied to DNA project diagrams created by Project Administrators utilizing specialized software. 

Polymorphism - See mutation.


RAO - Acronym for Recent Ancestral Origins (formerly known as REO - Recent Ethnic Origins)
The number of matches you have in Family Tree DNA's database as specified by country or region.  To access the RAO, Family Tree DNA clients need to click the tab on their "My FTDNA" page.

recLOH - Acronym for Recombinant Loss of Heterozygosity - When a section of DNA on a marker is missing, that marker is sometimes repaired by another marker filling in the missing DNA with its own material. This is referred to as a "recLOH event" and is usually observed with multi-copy markers like 385a and 385b, and is also common in the 464 set.  The recLOH event causes the allele values to match 11-11 instead of the more common, 11-14 that you see in R1b.  For more about: Recombinational Loss of Heterozygosity (recLOH)

Recombination - An event occurring during meiosis - the formation of sperm and egg cells. One chromosome from the mother and the other from the father break and trade segments with one another.

Replication - See DNA replication.

Restriction enzyme - A protein that recognizes a certain sequence of DNA and cuts the DNA at that site.

Restriction Fragment Length Polymorphism (RFLP) - See single nucleotide polymorphism.


Sequencing - See DNA sequencing.

Sex chromosome - The X- or Y-chromosome. Normally males have one X and one Y and females have two Xs.

SNP - (pronounced SNIP) - Acronym for Single Nucleotide Polymorphism.  A SNP test confirms your haplogroup by determining if a SNP has mutated from its derived or ancestral state.  A SNP is usually found on a different area of the Y-chromosome than where the YSTR markers are.  Sometimes, a SNP may cause a null result on a marker.

STR - Acronym for Short Tandem Repeat - See: YSTR

Sub-clade - Referring to a "branch" farther down the phylogenetic tree.  Example: H3 -> '3' is a sub-clade of mitochondrial haplogroup 'H'.  R1b -> '1b' is a sub-clade of Y-chromosome haplogroup 'R'.  Sub-clade testing is also referred to as deep clade testing.

Surname - A last name or family name traditionally passed down from father to son.


Time to the Most Recent Common Ancestor (TMRCA) - The amount of time or number of generations since individuals have shared a common ancestor. Since mutations occur at random, the estimate of the TMRCA is not an exact number (i.e., 7 generations), but rather a probability distribution. As more information is compared, the TMRCA estimate becomes more refined.

Transmission event - The passage of genetic material from one generation to the next.


Unique Event Polymorphism (UEP)  See single nucleotide polymorphism


Western Atlantic Modal Haplotype (WAMH)  The most common Y-DNA haplotypes found in Europe’s most common Y-DNA haplogroup, R1b.

Whit's Predictor - The commonly applied nickname to the "Y-Haplogroup Predictor" created by Whit Athey.  Enter Y-chromosome markers into the predictor and it will display percentages for matches to various haplogroups.


X-chromosome - The female gender chromosome, if a child receives one X from the father and one X from the mother, the child's gender is female.


Y-Base - A free public database sponsored by DNA Heritage where Y-chromosome DNA results from any testing facility may be uploaded and compared.

Y-chromosome - The male gender chromosome.  In other words, only males have a Y-chromosome, which they receive from their father, who received it from his father, and so on.  This transmission of the Y-chromosome down the male line is why it is useful for surname testing to determine if two males share a common ancestor.

Y-DNA phylogenetic tree - A graphic representation of the Y-DNA haplogroups according to the YCC classification. Haplogroup names and major clades are labeled and mutation names are given along the branches of the trees.

Y-Search - A free public database sponsored by Family Tree DNA where Y-chromosome DNA results from any testing facility may be uploaded and compared.

YSTR - Acronym for Y-chromosome Short Tandem Repeat.  The number of times the bases repeat that determines the value of the marker.  Example: Thirteen repeats of the same bases equals a value of '13'.


Glossary Websites:

Kerchner's Genetic Genealogy Glossary
National Geographic Genographic Project Genetics Glossary
Family Tree DNA Glossary
Genetics/DNA Glossary - Clan Lindsay
ISOGG's Y-SNP Tree Glossary of Genetics Terms

To purchase a comprehensive published glossary:
Genetic Genealogy DNA Testing Dictionary 



Contribution credits: 
K. Borges, C. Mello, 
P. Goff, E. Krause,
N. Custer.

Copyright © 2006
All Rights Reserved
Compiled: 05/17/06

Page last updated: 12/04/2007

Used with ISOGG's permission