Genetic genealogy has a number of terms that may be unfamiliar to genealogists who haven’t dabbled in DNA testing. To help you unpack these terms, this section contains a glossary of key terms used throughout the book, featuring a brief definition and a reference to the chapter in which the term first appears. Note these key terms may also appear in chapters other than the one referenced here.
admixture: Combination of different genetic lineages, usually with different geographic origins (chapter 9)
ancestral: Designation indicating the test-taker has an ancestral SNP value (i.e., no mutation) at a particular location (chapter 5)
autosomal DNA (atDNA): One of the four kinds of DNA useful to genealogists, found in the nucleus and comprising the twenty-two non-sex chromosomes (chapter 1)
autosome: One of the twenty-two non-sex chromosomes in the human genome (chapter 6)
Cambridge Reference Sequence (CRS): The first mtDNA sequence published; the long-time standard against which all test-takers’ mtDNA are compared (chapter 4)
chromatin: Tight bundle of DNA and proteins that forms chromosomes; could be subject of future DNA testing (chapter 12)
chromosome: Structure containing millions of DNA base pairs; humans have a total of forty-six chromosomes, organized into twenty-three pairs (chapter 1)
chromosome browser: Tool that lets test-takers see exactly what segment(s) of their chromosomes are shared with another test-taker (chapter 6)
chromosome pair: Two complementary chromosomes that come together to form a pair (chapter 1)
coding region (CR): Region of mtDNA that contains genes and instructions for the cell and thus rarely changes; has only recently been included in mtDNA testing (chapter 4)
derived: Designation indicating the test-taker has a mutation at a particular SNP location (chapter 5)
DNA (deoxyribonucleic acid): Molecule that contains genetic information and can be a valuable tool for genealogists; two long chains containing millions of base pairs that form a double-helix structure (chapter 1)
ethnicity estimate: Method of inferring the geographical origins of an individual’s DNA by comparing that DNA to one or more reference populations (chapter 9)
fully identical region (FIR): Portion of genome where two people share a segment of DNA on both of their chromosomes (chapter 6)
gene: Region of DNA that contains genetic information or instructions utilized by the cell, such as for the creation of proteins needed for life (chapter 1)
genealogical family tree: Collection of all an individual’s ancestors, regardless of whether or not they contributed DNA to the individual (chapter 1)
genetic distance: Numerical representation of the differences or mutations between two individuals’ Y-DNA or mtDNA results (chapter 4)
genetic exceptionalism: The theory that genetic information is unique and should be treated differently than other kinds of genealogical evidence (chapter 3)
genetic family tree: Collection of genealogical ancestors that contributed DNA to a genome; a subset of the genealogical family tree (chapter 1)
genetic genealogy: The practice and study of using DNA in genealogical research (chapter 1)
Genetic Genealogy Standards: Set of ethical principles and best-practices established by an ad hoc committee of scientists and genealogists (chapter 3)
half-identical region (HIR): Portion of genome where two people share a segment of DNA on just one of their two chromosomes (chapter 6)
haplogroup: Group of individuals who share several genetic mutations as well as a common (usually ancient) ancestor; exist on two genetic lines: mtDNA and Y-DNA (chapter 4)
haplotype: The collection of specific marker results that characterize a test-taker (chapter 5)
heteroplasmic: Containing more than one sequence of mtDNA within a cell or organism (chapter 4)
homoplasmic: Containing only one sequence of mtDNA within a cell or organism (chapter 4)
hypervariable control region 1 (HVR1): One of the two regions of mtDNA that frequently undergoes changes between generations and thus is often sampled in mtDNA testing (chapter 4)
hypervariable control region 2 (HVR2): One of the two regions of mtDNA that frequently undergoes changes between generations and thus is often sampled in mtDNA testing (chapter 4)
karyotype: All of the chromosome pairs in a human cell arranged in a numbered sequence from longest to shortest (chapter 1)
marker: An assigned, commonly tested region of DNA (chapter 2)
meiosis: A specialized process in which cells divide as eggs and sperm are created for reproduction (chapter 6)
mitochondria: Energy-producing units that live within cells and are inherited from the mother, where mtDNA is found (chapter 1)
mitochondrial DNA (mtDNA): One of the four kinds of DNA useful to genealogists, found in the mitochondria of a cell and always inherited from the mother (chapter 1)
most recent common ancestor (MRCA): The ancestor who is shared by two or more individuals and was born most recently (chapter 4)
mtDNA sequencing: One of the two kinds of mtDNA testing; examines part or all of an mtDNA nucleotide base pairs (chapter 4)
mutation: Any variance in DNA that occurs between individuals or between an individual and a reference sequence (chapter 4)
non-coding regions: Portions of the human genome that do not contain genetic information (chapter 1)
non-paternal events: Events or circumstances such as adoption, name change, or infidelity that lead to an unexpected break in a genetic line (chapter 2)
nonsister chromatids: Copies of non-identical chromosomes that have been duplicated during meiosis; any crossover/recombination between these two results in distinguishable mutations in the DNA (chapter 6)
nucleotide: Organic building blocks that form pairs to create DNA molecules; the four varieties are found in human DNA are adenine, cytosine, guanine, and thymine (chapter 1)
nucleus: Control center of cells, where most DNA is found (chapter 1)
phasing: Method of separating an individual’s DNA into the DNA inherited from the mother and the DNA inherited from the father (chapter 9)
recombination: Process by which chromosome pairs exchange genetic material, leading to variations between generations (chapter 4)
Reconstructed Sapiens Reference Sequence (RSRS): Recent effort to represent a single mtDNA genome of all living humans; sometimes used as the standard against which test-takers’ mtDNA is compared (chapter 4)
reference population: Group(s) of people to whom test-takers’ results are compared (chapter 2)
revised Cambridge Reference Sequence (rCRS): An update to the CRS; commonly used as the standard against which test-takers’ mtDNA is compared (chapter 4)
segment triangulation: Method of tracing one or more segments of an individual’s DNA back to a specific ancestor or ancestral couple by comparing the DNA to that of two or more genetic relatives who all share the same segment of DNA and ancestor (chapter 10)
single nucleotide polymorphism (SNP): Single nucleotide in the DNA sequence that can differ between individuals in a population (chapter 4)
sister chromatids: Identical copies of a chromosome that has been duplicated during meiosis (chapter 6)
SNP testing: One of the two kinds of mtDNA testing; examines specific locations (SNPs) along the circular mtDNA molecule (chapter 4)
subclade: Subgroup of a haplogroup, defined by one or more SNP mutations (chapter 5)
tree triangulation: Method for finding ancestors by using other individuals’ family trees in conjunction with genetic in-common-with tools (chapter 10)
whole-genome sequencing: Testing that examines all of an individual’s DNA (chapter 6)
X-chromosomal DNA (X-DNA): One of the four kinds of DNA useful to genealogists, found on the X chromosome (chapter 1)
X chromosome: One of the two sex chromosomes that determine gender, among other traits; two X chromosomes (one inherited from each parent) result in the individual being female (chapter 7)
Y-chromosomal DNA (Y-DNA): One of the four kinds of DNA useful to genealogists, found on the Y chromosome that only males have and inherited only from the father (chapter 1)
Y-chromosome: One of the two sex chromosomes that determine gender, among other traits; one X chromosome (inherited from the mother) and one Y chromosome (inherited from the father) result in the individual being male (chapter 5)
Y-SNP testing: One of the two kinds of Y-DNA testing; examines specific locations (SNPs) along the Y-chromosome (chapter 5)
Y-STR testing: One of the two kinds of Y-DNA testing; examines short, repeating sequences of DNA (STR, or short tandem repeat) along the Y-chromosome (chapter 5)