A Genetic Genealogy Glossary

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

 

A

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 Composition — name for the admixture report at 23andMe

AncestryDNA — a genetic genealogy testing company that offers autosomal DNA tests

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)

 

B

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

 

C

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

 

D

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

 

E

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

 

F

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

Family Tree DNA — a genetic genealogy testing company that offers autosomal, mitochondrial, and yDNA tests (abbreviated FTDNA)

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)

 

G

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

 

H

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

 

I

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

 

J

K

L

likelihood — see maximum likelihood

M

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)

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 genetic genealogy testing company that offers autosomal DNA tests

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

 

N

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)

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)

 

O

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)

 

P

PAR — abbreviation for pseudoautosomal region

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

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

 

Q

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

 

R

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

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)

 

S

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

 

T

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

 

U

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

 

V

W

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

 

X

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

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

yDNA — DNA on the Y chromosome

 

Z

 

Numbers

23andMe — a genetic genealogy testing company; a genetic genealogy testing company that offers autosomal DNA tests and haplogroup assignments

 

Still To Be Defined

ethnicity

Evil Twin

excess IBD

haplotype —

heteroplasmy

heterozygosity

homozygosity —

imputation

institutional review board — (abbreviated IRB)

Lazarus

linkage disequilibrium

most distant known ancestor — (abbreviated MDKA)

most recent common ancestor — (abbreviated MRCA)

microarray

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

pseudoautosomal region — (abbreviated PAR)

polymorphism

population

recombination

reference panel

 

Dodecad

Ethiohelix —

Eurogenes —

GedrosiaDNA —

HarappaWorld —

MDLP Project —

PuntDNAL —

 

 

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