Genetics Glossary

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This is a glossary of terms commonly used in the study of genetics and genetic genealogy. For more specific details, please see the article corresponding to each term where available.

Contents Top · 0–9 · 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

0-9

A

  • Adenine: One of the four nucleotide bases in DNA or RNA; pairs with thymine in DNA or uracil in RNA.
  • Allele: An allele (pronounced UH-leel is one of multiple alternative forms of a single gene, each of which is a viable DNA sequence occupying a given position, or locus on a chromosome. For example, in humans, one allele of the eye-color gene produces blue eyes and another allele of the eye-color gene produces brown eyes.
  • 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.
  • Affected relative pair: An affected relative pair consists of two organisms related genetically that are both affected by the same trait. For example, two cousins who both have blue eyes are an affected relative pair since they are both affected by the allele coding for blue eyes.
  • Ancestral haplotype: The haplotype of a MRCA deduced by comparing descendants' haplotypes and eliminating mutations.
  • 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.
  • Ancestry-informative markers
  • Ancient DNA
  • 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.
  • Archaeogenetics
  • Atlantic Modal Haplotype (AMH): See Western Atlantic Modal Haplotype.
  • Autosomal DNA: The DNA of non-sex-determining chromosomes that mix or recombine. Also known as admixture DNA.

B

  • Base pair: A pair of nucleotide bases on complementary DNA or RNA strands organized in a double helix.
  • Bikini haplotypes: Minimal haplotype data, i.e.: six Y-STR markers.
  • Biogeographical analysis (BGA)
  • Buccal cell: A type of cell found in cheek tissue inside the mouth.
  • Build: The term used for the human genome reference standard (Build 38 is the most recent reference genome).

C

  • Cambridge Reference Sequence (CRS): The first mitochondrial DNA to be fully sequenced at Cambridge University in 1981.
  • CCR5: A gene located on chromosome 3.
  • Centimorgan
  • Centromere
  • Chromosome: A molecular "package" for carrying DNA in cells, organized as two double-helical DNA molecules that encode many genes. Some simple organisms have only one chromosome made of circular DNA, while most eukaryotes have multiple chromosomes made of linear DNA.
  • Chromosome mapping
  • Cladogram
  • Coalescence age: The merging of genetic lineages backwards in time to the most recent common ancestor (MRCA).
  • Coding region: A region of DNA which contains genes.
  • CODIS: Acronym for Combined DNA Index System - the FBI's autosomal STR DNA database for profiles of criminal offenders.
  • 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.
  • 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 haplotypes changing over time to resemble one another.
  • Crossover: See: Recombination.
  • Cytosine: One of the four nucleotide bases in DNA or RNA; pairs with guanine.

D

  • D9S919: A Y-STR marker on chromosome 9.
  • Deoxyribonucleic acid (DNA) A chemical consisting of a sequence of hundreds of millions of nucleotides found in the nuclei of cells containing the genetic information about an individual. It is shaped like a double-stranded helix, which consists of two paired DNA molecules and resembles a ladder that has been twisted. The "rungs" of the ladder are made of base pairs, or nucleotides with complementary hydrogen bonding patterns.
  • Deletion
  • Derived state: Refers to the state of a Y-chromosome SNP that has mutated, usually in one man, from the ancestral state and created a new haplogroup or subclade 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 Newbie: 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.
  • 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.
  • Discord
  • 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. It is assigned based on a nomenclature system controlled by the HUGO Gene Nomenclature Committee, which assigns DYS numbers to newly discovered markers.

E

  • Electropherogram
  • Endogamy: The practice of marrying within the same ethnic, cultural, social, religious or tribal group.
  • Enzyme: A protein that facilitates a specific chemical reaction by working as a catalyst.
  • Epigenome
  • Exact match: Two individuals with exactly the same results for all markers or regions compared.

F

G

  • 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.
  • Gene: A segment of DNA which contains the genetic code to make a certain protein or part of a protein.
  • Gene expression: The process in which the information encoded in a gene is converted into a form useful for the cell. The first step is transcription, which produces a messenger RNA molecule complementary to the DNA molecule on which a gene is encoded. For protein-coding genes, the second step is translation, in which the messenger RNA is read by the ribosome to produce a protein.
  • Gene pool: The sum of all the alleles shared by members of a single population.
  • 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. See: Generation length.
  • Generation length
  • Genetic ancestry
  • Genetic anthropology
  • Genetic cousins: Individuals whose Y-DNA, mtDNA or autosomal DNA test results match one another.
  • Genetic determinism: The belief that genes alone determine the physical and mental characteristics of a child.
  • 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 drift
  • Genetic exceptionalism: The belief that genetic information is special and needs to be treated in a different way from other medical information.
  • Genetic genealogy: The use of DNA testing in combination with traditional genealogical and historical records to infer relationships between individuals.
  • Genetic genealogist: A genealogist who is involved in genetic genealogy.
  • Genetic paternalism: The belief that genetic tests for health purposes should be ordered through a medical professional for the protection of the individual.
  • Genetic signature: Another name for a haplotype.
  • Genetics: The field of biology that studies genes and their inheritance; the study of DNA.
  • Genome: The entire complement of genetic material in the chromosome set of an organism, virus or organelle. The human genome is composed of 46 chromosomes, with a total of 3 billion base pairs.
  • Genotype: The complement of alleles present in a particular individual's genome that give rise to the individual's phenotype.
  • Gigabase
  • Guanine: One of the four nucleotide bases in DNA or RNA; pairs with cytosine.

H

  • Half-identical region: A half-IBD segment where your genotype matches (at least) half of another person's genotype.
  • Haplogroup: A group of similar haplotypes that share a common ancestor with a SNP mutation. Because a haplogroup consists of similar haplotypes, it is 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: R1b1a. Y-chromosome and mitochondrial DNA haplogroups have different haplogroup designations. Haplogroups pertain to your deep ancestral origins dating back thousands of years.
  • Haplotree: A haplogroup tree. A diagram or chart showing the different lineages within a haplogroup.
  • Haplotype: The term for the set of numbers that consists of your Y-chromosome or mitochondrial DNA results. Haplotypes are also known as genetic signatures.
  • Heteroplasmy
  • Heterozygous
  • Holliday junction: A mobile junction between four strands of DNA.
  • Homozygous
  • Hypervariable region (HVR): The sections of non-coding mitochondrial DNA that are used for low-resolution genealogical DNA tests.

I

J

K

L

M

  • Male-specific Y: Another name for the non-recombining region of the Y-chromosome.
  • Marker: A specific place on a chromosome with two or more forms, called alleles, the inheritance of which can be followed from one generation to the next. In Y-chromosome DNA testing, this refers to non-coding Y-chromosome DNA. Numbers designate the individual DNA segments. Example: 393=13. This means at marker #393, your allele value is 13.
  • Massively parallel sequencing: See: Next generation sequencing.
  • Match
  • Matriline
  • Megabase
  • Meiosis The stage in which sperm and egg cells are formed. It is during this process that the autosomal chromosomes recombine and mutations occur.
  • Micro-allele
  • Microsatellite: Another name for a 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.
  • Mitochondrial Eve: The common matrilineal ancestor of all living humans.
  • Mitosearch: Mitosearch is a free public database sponsored by Family Tree DNA where mitochondrial DNA results from any testing facility may be uploaded and compared.
  • Mitosis
  • Modal haplotype
  • Most recent common ancestor (MRCA): The most recent ancestor from whom a group of individuals share descent.
  • Mutation: A change in the DNA that occurs spontaneously. Mutation is a scientific term that often connotes a negative connotation as a result of 1950s 'B' movies, but in genetic genealogy, mutations are utilized for distinguishing different ancestral lines. Mutations can also occur due to environmental factors, such as exposure to radiation.
  • Mutation rate: The frequency with which random mutations occur.

N

  • Next generation sequencing (NGS)
  • Non-coding DNA: Also referred to as 'junk DNA', non-coding DNA is not part of an active gene that contains a code for making a protein. Recent evidence shows that at least some non-coding DNA is involved in biological processes such as regulation of gene expression and chemical signalling among cells.
  • No call
  • Non-paternity event (NPE): An event which has caused a break in the link between the surname and the Y-chromosome resulting in a son using a different surname from that of his biological father (eg, illegitmacy, adoption, maternal infidelity).
  • Non-recombining Y (NRY): The section of the Y-chromosome that is passed from father to son down the patriline. While it does not recombine, it does have mutations over time.
  • Nuclear DNA: The DNA of chromosomes found in the nucleus of the cell.
  • Nucleotide: One of the four monomers that make up a DNA molecule.
  • Null value: 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 Y-STR markers have been identified in certain families to have null results (for example, DYS439, and DYS448)

O

P

  • Palindrome: A double-stranded DNA segment in which the sequence of one strand is in the reverse order to the other strand. Example: DYS464X where a family line in haplogroup R1b1a2 has cccc or ccgg instead of the usual cccg pattern.
  • Patriline
  • Pedigree collapse
  • Personal genomics
  • Phasing: The task or process of determining the parental source of a SNP's alleles (i.e., determining which parent contributed each specific allele)
  • Phenotype: The observable physical or behavioral traits of an organism, largely determined by the organism's genotype.
  • Pherogram: For STRs, a plot which shows the length of a fragment of DNA. This allows its allele value to be measured.
  • Phylogeography
  • Phylotree: A shortened term for phylogenetic tree. It is most often used in reference to the available online diagrams showing the Y-chromosome and mitochondrial DNA haplotrees. This term is also applied to DNA project diagrams created by Project Administrators utilizing specialized software. Phylotree is also a website which hosts the mtDNA evolutionary tree and a minimal reference version of the Y-SNP haplotree.
  • Polymorphism: See: Mutation.
  • Poor man's phasing: The process of phasing by using siblings, aunts and uncles or other close relatives as a proxy for a parent.
  • Protein: A linear polymeric molecule made of amino acids linked by peptide bonds. Proteins carry out the majority of chemical reactions that occur inside the cell.
  • Proxy: Usually used in reference to the contact person for a DNA test. Example: A female who has tested a male relative.
  • Pseudogene: A gene which has lost its function over time.
  • Pseudophasing: The process of phasing by inference from population reference samples.
  • Pseudosegment: A false positive matching segment which occurs as a result of matching alleles zig-zagging backwards and forwards between the maternal chromosome and the paternal chromosome. Also known as a false segment, a spurious segment, an erroneous segment or a phantom segment.

R

  • 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 multicopy 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.
  • 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.
  • Reconstructed Sapiens Reference Sequence: The inferred mitochondrial DNA ancestral sequence.
  • 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.
  • Revised Cambridge Reference Sequence: A revised version of the Cambridge Reference Sequence. Mitochondrial DNA results are compared against the rCRS.

S

T

  • Thymine: One of the four nucleotide bases in DNA; pairs with adenine. In RNA, thymine is replaced with uracil.
  • TiP: Acronym for the Family Tree DNA Time Predictor tool - a proprietary program created by Family Tree DNA to calculate the time to the most recent common ancestor using mutation rates specific to each marker.
  • 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.
  • Transcription: The first step in gene expression, in which a messenger RNA molecule complementary to a particular gene encoded in DNA is synthesized by enzymes called RNA polymerases. To produce a functional protein, transcription is followed by translation.
  • Translation: The second step in gene expression, in which a messenger RNA molecule is read by the ribosome to produce a functional protein. Translation is always preceded by transcription.
  • Transmission event: The passage of genetic material from one generation to the next.
  • Triangulation: A method of determining the ancestral haplotype of an ancestor using the DNA results of direct line descendants.

U

  • Unique-event polymorphism
  • Uracil: One of the four nucleotide bases in RNA; pairs with adenine. In DNA, uracil is replaced with thymine.

W

X

  • X-chromosome: A sex chromosome. A female child receives one X-chromosome from her father and one X-chromosome from her mother. A male child receives an X-chromosome from his mother and a Y-chromosome from his father.

Y

  • Y Alu Polymorphism (YAP): An alu is a sequence of approximately 300 letters (base pairs) which has inserted itself into a particular region of the DNA. A Y alu polymorphism is an alu which has occurred on the Y-chromosome. There are about a million Alu insertions scattered throughout the human genome.
  • Y chromosome: The male sex chromosome. 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-chromosomal Adam: Also known as Y-Adam. The common patrilineal ancestor of all living males.
  • Y Chromosome Consortium (YCC)
  • Ysearch: Ysearch is a free public database sponsored by Family Tree DNA where Y-chromosome DNA results from any testing facility may be uploaded and compared.
  • Y-STR: 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'.

Acknowledgements

This glossary includes the content from the ISOGG DNA Newbie Glossary which was previously published on the main ISOGG website (for reference see the version preserved in the Internet Archive in August 2014). The ISOGG DNA Newbie Glossary was compiled on 17 May 2006, revised on 13 January 2008, and last updated on 7 December 2009. The content from the Newbie Glossary was incorporated into the ISOGG Wiki Glossary on 25 January 2015. The contributors to the original ISOGG DNA Newbie Glossary were: K. Borges, N. Custer, P. Goff, J. Hailman, E. Krause and C. Mello.

Links to other glossaries

See also