The subject of DNA introduces many terms that may not be familiar to most family historians. A brief glossary of DNA terms has been added to make the learning process easier. When a new term is first used on the project web page it will appear with a link to the glossary. For more detailed technical definitions, see the Charles Kerchner's Genetic Genealogy Glossary.

A | B | C | D | E | G | H | J| M | N | P | R | S | T | W | X | Y



Adenine is the "A" of the four bases that make up DNA. Adenine is always paired with thymine.


A DNA sequence that repeats at a certain locus or place on the string of DNA. The allele value is the number of times the sequence repeats. Pronounced uh-LEEL.


The study of human origins using DNA testing and genealogical methods.


The study of man kind, particularly in terms of its origin and culture.



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.



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.


The "C" of the four bases that make up DNA. The other bases are adenine (A), guanine (G), and thymine (T). Cytosine always pairs with guanine.


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.

DNA amplification

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

DNA sequencing

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

Double helix

The twisted shape DNA forms when its two strands bond together. A double helix looks like a twisting or rotating ladder.

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.


Exact match

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


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.



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

Genealogical Data Communication (GEDCOM)

A type of file format used by genealogical software to make your family tree. You can upload your GEDCOM file to your Family Tree DNA personal page as well as Ysearch or mitosearch. Learn more about GEDCOM here

Genealogical Timeframe

Time period in which genealogical records can be found. Usually considered to be the past 500 years although in some cases records can be found as far back as 1,000 years.


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. The most commonly used time period is 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 DNA results. A genetic distance of zero means there are no differences in the results being compared against one another.


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

Genographic Project

Research study sponsored by the National Geographic Society and IBM to use DNA to determine human origins and migration patterns.


The genetic makeup of an individual organism.

Glacial maximum

The scientific term for the peak of an ice age.


The "G" of the four bases that make up DNA. The other bases are adenine (A), cytosine (C), and thymine (T). Guanine always pairs with cytosine.



A haplogroup is a large cluster of people who share a common DNA heritage. It is a genetic population group associated with early human migrations and which can today be associated with a geographic region. It has been compared to a major branch on the human family tree. Even though female and male haplogroups may have the same letters, their definitions are different.


One person's set of values for the markers that have been tested. Two individuals that match exactly on all markers have the same haplotype. It has been compared to the leaves on the human family tree.

Human Genome Project

Significant 13 year project funded by the United States, Japan, France, Germany and China as well as private donors to document each of the 3.2 billion base pairs that make up human nuclear DNA. Although most of the project was completed in 2003, analysis of the data will continue for several years.


Junk DNA

Also called non-coding DNA. Sections of DNA that do not code for genes. Most of the genome consists of non-coding DNA, and was therefore long thought to be 'junk.' Scientists have found that in addition to containing markers that are helpful for genetic genealogy, parts of these non-coding regions have regulatory and other functions.



A physical location (locus) on the chromosome.


See short tandem repeat.


A specific organelle in the cell that helps it to produce energy. Each cell contains several mitochondria.

Mitochondrial DNA (mtDNA)

The genetic material found in mitochondria. It is passed down from females to both sons and daughters, but sons do not pass down their mother's mtDNA to their children. It is less useful in tracing family relationships than the Y-Chromosome because of its slow mutation rate. It is useful in population studies in tracking "deep ancestry" (ancestry thousands or years ago).

Modal haplotype

The most common result for each marker tested in a group of results.

Most Recent Common Ancestor (MRCA)

The ancestor shared most recently between two individuals.


A heritable change that occurs in genetic material. It may lead to a different number of repeats of a certain sequence or a change in one of the bases in a sequence.

Mutation rate

The frequency with which random mutations occur.


Non-paternity event

Term used by genetic anthropologists to describe situations where the biological relationship is not consistent with the written record. This includes adoptions, illegitimacies, and births where the father can not be determined.


A piece of DNA that contains one base, one phosphate group, and one sugar unit. Thousands of nucleotides joined in sequence make a molecule of DNA.


The membrane-bound organelle containing the chromosomes.

Nuclear DNA

DNA found in the nucleus of the cell. It consists of 23 pair of chromosomes and is responsible for coding who we are.


Phylogenetic tree

See Y-DNA phylogenetic tree.

Polymerase Chain Reaction (PCR)

A technique allowing the production of multiple copies of extremely small amounts of DNA fragments using DNA polymerase and specific primers.


See mutation.


Restriction Fragment Length Polymorphism (RFLP)

See single nucleotide polymorphism.



See DNA sequencing.

Sex chromosome

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

Short Tandem Repeat (STR)

A short DNA pattern of repeated bases. "GATA" repeated eleven times would give the marker a value or allele of 11.

Single Nucleotide Polymorphism (SNP)

A change in the DNA that happens when a single nucleotide (A, T, G, or C) in the genome sequence is altered.



The "T" of the four bases that make up DNA. The other bases are adenine (A), cytosine (C), and guanine (G). Thymine always pairs with adenine.

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, but rather a probability distribution. As more information is tested, the TMRCA estimate becomes more refined. A 67 marker test will yield a more reliable estimate than a 37 marker test.


Unique Event Polymorphism (UEP)

See single nucleotide polymorphism.

Undocumented Paternity Event

See non-paternity event.


Western Atlantic Modal Haplotype (WAMH)

The most common Y-DNA haplotypes found in Europe’s most common Y-DNA haplogroup, R1b.



One of the two sex chromosomes, X and Y. X is the sex chromosome that is present in both sexes: singly in males and doubly in females.



One of the two sex chromosomes, X and Y. It is the Y-chromosome that makes a person a male. The Y-chromosome passes down from father to son. Females do not receive it. The fact that the Y-chromosome goes down the paternal line makes it valuable for genealogy studies, since it typically follows a surname line.


The Y-Chromosome Consortium. A body of scientists responsible for naming Y haplogroups and specifying the mutations defining each group.

Y-DNA phylogenetic tree

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