(Courtesy of the National Human Genome Research Institute and AncestryDNA.com)


An allele is a variation at a specific location along the genetic code. As a simplified example, at the locus that contains the code for eye color, some people have the allele for blue eyes, and others have the allele for brown eyes. When comparing individuals to determine they share a common ancestor, the allele values at each of the tested loci (also known as markers) are compared.

Autosomal DNA

Of the 23 pairs of chromosomes in humans, 22 are autosomal (the other pair being sex chromosomes). Autosomal DNA gets shuffled and recombined in the process of sexual reproduction, unlike Y-DNA and mitochondrial DNA (mtDNA) which are passed on relatively unchanged onto the next generation. Most of your physical characteristics come from your autosomal DNA; however, this personal genetic information is neither relevant nor tested for in genetic genealogy. In genealogical autosomal DNA tests, only the non-coding DNA is examined

Base Pair

The DNA molecule takes the form of a double helix, which looks like a twisted ladder. Each rung of the ladder is a base pair, two nucleotides (also called bases) that are bonded together. The 23 chromosomes of human DNA (if you imagine laying them out end to end) are estimated to be about 3 billion base pairs long.

Centimorgan (cMs)

A centimorgan (abbreviated cM) or map unit (m.u.) is a unit for measuring genetic linkage (the tendency of genes that are located proximal to each other on a chromosome to be inherited together during meiosis). It is defined as the distance between chromosome positions (also termed, loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01. It is often used to infer distance along a chromosome.


A chromosome is a unit of DNA, a structure containing genetic material. There are two basic types of chromosomes: autosomes and sex chromosomes. Humans have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes. In females the 23rd chromosome pair consists of two X-chromosomes. Males, however, have an X-chromosome and a Y-chromosome. Therefore, it is the Y-chromosome that determines the male gender. Each chromosome contains hundreds to thousands of genes.

CRS (Cambridge Reference Sequence)

This term is only applicable to mitochondrial DNA. Researchers at Cambridge University, led by Dr. Frederick Sanger, were the first to sequence the mitochondrial genome. They chose one female individual of European descent. The CRS has since been revised and the revised Cambridge Reference Sequence (rCRS) is the reference standard against which allmtDNA sequences are compared.

DNA (Deoxyribonucleic Acid)

DNA is found in every cell in your body except the mature red blood cells. It is located in a part of the cell called the nucleus. DNA contains all the information necessary to create your body and help it to coordinate the functions of your body from wiggling your toes to operating your heart. Some of your DNA also has information on your genetic heritage. The three types of DNA that are used in genealogy are autosomal,mtDNA, and Y-chromosomal.

DYS (DNA Y-Chromosome Short tandem repeat)

This term is only applicable to Y-DNA. Certain segments of the Y-chromosome repeat a short pattern which makes them easy to identify. These STR segments repeat a different number of times in different individuals, but at the same locus on the chromosome. Your Ancestry Y-DNA test results will give you either 33 or 46 DYS values, depending on which test you have purchased. Other companies may test different amounts or locations, but Ancestry’s DNA site will still allow you to enter these results if you have purchased a test from another company.


Genes are segments of DNA. There is no set length of code that makes up a gene, but rather they are delineated based on what they do: provide instructions for building proteins. The portions of DNA tested by Ancestry.com are non-genetic (non-coding DNA) in nature.


While not directly genealogically (recent past) relevant, haplogroups are instead anthropological (ancient past) in nature. Your Ancestry DNA results will include a predicted haplogroup and information on its anthropological history. Remember how exciting it was to discover on which ship your ancestors immigrated to America? Your DNA results take you back even further; you’ll be able to read about the migrational path that your distant ancestors initially took out of Africa. Humans began to diversify as they migrated out of Africa and populated the rest of the world adapting to new climates, diets, and living conditions. Over tens of thousands of years, these ancient populations became isolated. Each population’s DNA changed as they became more adapted to their environment until they became genetically distinct from one another. Today, these deep ancestral groupings are referred to as haplogroups. We are able to predict your haplogroup based on your haplotype, but to confirm your haplogroup you will need a SNP test.


Your haplotype is your unique DNA profile. It is determined by examining the variations (alleles) present at certain short tandem repeated (STR) loci and can be used to disprove relatedness to others, or establish that they may be related if their test results indicate their haplotype is the same or very similar to your own (we refer to these as matches). Others with haplotypes similar to yours will be in your haplogroup, a geographically based collection of individuals with genetic similarities.


This term is only applicable to mitochondrial DNA. Due to the vast amounts of mitochondria in our cells, it is possible that some contain slightly different DNA than others. The mtDNA test will pick up any variations (alleles) at tested locations and report both. For example, a result of ‘R’ at a particular markers means you had the heteroplasmy of one copy of ‘A’ and one copy of ‘G’ at that location.

HVR (Hyper-Variable Region)

This term is only applicable to mitochondrial DNA. Because mtDNA is passed on almost completely unchanged from one generation to the next, the most informative part of the DNA to examine is the part that changes the most. These hyper-variable regions, or HVRs, have the highest rate of change in the entire mtDNA molecule, although the changes still happen incredibly infrequently (about one every 10,000 years). Tracking these changes allows you to trace your deep ancestral heritage and give you information on your predicted maternal haplogroup. Ancestry’s mtDNA test examines HVR1 and HVR2, and you can compare your results against our database to see others whose results matches your own. If you have taken another company’s mtDNA test, you can manually enter the results for HVR1, HVR2, and/or HVR3.



IBD = Identical By Descent, you inherited a segment of DNA from a parent.
IBS = Identical By State, a very small segment from your mother aligns with a small segment from your father and the computer reads it as a match with some other person. These are also know as "False positives".

“Junk” DNA

Junk is a bit of a misnomer, because this is the part of your DNA that provides the most genealogical information. Scientists refer to junk DNA to differentiate it from the portion of DNA that contains genetic coding instructions. This is one case where one man’s trash is another man’s treasure! Coding DNA has information like eye color, blood type, and susceptibility to disease; although scientifically interesting, this makes coding DNA unique to you and useless for comparing yourself to potential ancestral matches. Ancestry only tests the non-coding DNA regions of your DNA, since these are the regions containing information on your heritage.


The particular region of the DNA that is analyzed is often referred to as a locus or marker. Locus is a singular location, and loci is the plural of this term.


Also known as loci, these are regions of DNA that have a signature or pattern that make them identifiable in all people. The differences in information at marker points are called alleles. This is the data upon which your matches are based.


These are other people that have either taken a DNA test from Ancestry.com or manually entered their DNA test results that they obtained from another source and have results in common with you. Your closest matches will be darker orange, while more distant matches fade from yellow to green.

Missing Teeth

Sometimes you will see a two DNA segments close together with a small slice missing. This is referred to as Missing Teeth. The approximate length of the segment is treated as the sum of the two segments.

MRCA (Most Recent Common Ancestor)

The most recent common ancestor is an estimated value that shows in which generation you may be able to find a common ancestor with your matches. The lower this number, the more closely related you might be to a person.

mtDNA (Mitochondrial DNA)

Mitochondrial DNA is different from the rest of your DNA, in that it comes from a different part of the cell. Most DNA is located in the center of the cell, the nucleus. MtDNA comes from a part of the cell called a mitochondrion (plural: mitochondria), which provides the cell with energy. Because of this difference, it doesn’t get recombined like most DNA and is passed on unchanged from a mother to her children. Any female children will in turn pass that unchanged DNA to their children, and so on down the maternal line. Ancestry’s mtDNA test examines two hyper-variable regions (HVRs) of the mitochondrial DNA, and allows you to compare your results with others who have taken a mtDNA test to find matches. Due to the extremely low rate of change in mtDNA, a nearly perfect match won’t be as helpful as a perfect match in finding people that share your genetic heritage.

NIST (National Institute of Standards and Technology)

The National Institute of Standards and Technology is a non-regulatory government agency which sets the industry standard for DNA tests. FTDNA, 23andMe and Ancestry.com adheres to these standards in their DNA products and services.

Non-coding DNA

Also known as junk DNA, non-coding DNA is the part of your DNA that Ancestry will be testing. It contains no personally identifiable or genetic information.


DNA is made up of four different bases, also known as nucleotides. They are usually referred to by the first letter of their names: Guanine, Cytosine, Adenine, and Thymine. These nucleotides are on either side of the twisted-ladder-shaped structure of the DNA molecule, and connect in pairs to make the rungs of the ladder. G & C always bond together, as do A & T. The sequence of letters in DNA is your genetic code, partially common to others that are related to you, but also containing uniquely personal sequences.

rCRS (Revised Cambridge Reference Sequence)

This term is only applicable to mitochondrial DNA. Researchers at Cambridge University, led by Dr. Frederick Sanger, were the first to sequence the mitochondrial genome. They chose one female individual of European descent. The CRS has since been revised and the revised Cambridge Reference Sequence (rCRS) is the reference standard against which all mtDNA sequences are compared. Having no differences from the rCRS is just as useful as having multiple differences. If the CRS had been created using a person of African or Asian descent, then your observable differences would be different. Having no differences from the rCRS helps narrow down maternal lineages and haplogroups.

SNP (Single Nucleotide Polymorphism)

Single Nucleotide Polymorphisms (SNPs, pronounced "snips") are single base pair changes that occur infrequently throughout the genome. SNP testing is available for mtDNA, and Y-chromosome. This testing can confirm an individual's deep ancestral grouping (or haplogroup), and allows us to track the branching of haplogroups and subgroups from our original African home, as well as help us to discover interesting facts about our own ancient ancestor's movements across time and geography. Please Note that Ancestry.com does not offer SNP testing, as it does not provide any genealogically relevant information.

STR (Short Tandem Repeat)

Some DNA segments contain a repeated pattern of nucleotides. These repeated patterns are consistently located in every person’s DNA, which makes them incredibly useful areas to look at in multiple individuals. Although the pattern and the location of the pattern is the same for everyone, the pattern is repeated a different number of times in different people. These variations, or alleles, are the results you will receive after taking a DNA test and will let you compare your personal haplotype with others to find potential matches.


The Y-chromosome is passed essentially unchanged from father-to-son. Specific portions of the Y-chromosome are analyzed and compared against other participants’ Y results. This is also known as a father-to-son test and will test paternal lineage. Ancestry offers two different Y-chromosome tests: one that tests 33 markers and another that tests 46 markers. Because the 46 marker test will contain more information you will be able to find more potential matches and examine them with greater accuracy.