A

Allele

One of several alternative forms of a gene or DNA sequence at a specific chromosomal location (locus). At each autosomal locus an individual possesses two alleles, one from each parent.

Amplification

The process of making identical genetic copies of a specific region of DNA.PCR is a powerful techniques for amplifying specific regions of DNA.

Ancestral Clan Mother

A woman who is considered to be the ancient maternal ancestor from whom all people in a particular haplogroup (clan) are descended.

Ancestry

A person’s line of descent.

Anthropology

The study of humankind, including the comparative study of societies and cultures, and the science of human zoology and evolution.

Atlantic Modal Haplotype or AMH

Most common haplotype found in Europe.

Autosomes

The non-sex chromosomes.Humans have 23 pairs of chromosomes within the nucleus.Chromosomes 1 through 22 are autosomal.The other pair has the special property of determining one's gender:XX in females and XY in males.

B

Base

Adenine (A), cytosine (C), guanine, (G) or thymine (T) are the four bases in the DNA.The chemical building blocks of DNA. These bases pair up to form the "rungs" of the DNA double helix.

Base Pair

The DNA bases are always held together in pairs by weak hydrogen bonds attaching to one of the strands in the DNA double helix. Adenine always pairs with thymine, and guanine always pairs with cytosine.

BLAST

A family of programs that search sequence databases for matches to a query sequence.

Buccal Swab

A technique for obtaining human cells by gently and painlessly scraping the inside of one's cheek with a sterile cotton or foam swab.

Cambridge Reference Sequence (CRS)

The first complete sequence of human mtDNA, published in 1981. Recently revised to correct minor errors in the initial sequence (revised CRS or rCRS). Each mtDNA haplotype is described by the differences it shows with the rCRS. The nucleotides of this standard molecule are numbered from 1 to 16569.The history of the sequence changes is described in the Mitomap website.

Chromosome

Long strands of DNA on which genes are found. Each human cell has 46 chromosomes in 23 pairs. One member of each pair is inherited from the mother, the other from the father. Mitochondrial DNA is inherited only from the mother.

Clade

A group comprising all the evolutionary descendants of a common ancestor. Also called "clan" or haplogroup.

Coalescence time

Time in the past at which two or more lines of descent split from a common ancestor.

Coding DNA

DNA that encodes the amino acid sequence of a protein, or for a functional mature RNA (transfer RNA or ribosomal RNA).

Codon

A nucleotide triplet that specifies an amino acid or a translation stop signal.

Complementary strands

Two nucleic acid strands are complementary in sequence if they can form a stable double-stranded structure. Base pairs are formed between adenine and thymine (AT) and guanine and cytosine (GC).The GC pairing has three hydrogen bonds and is thus stronger (i.e., requires more energy to melt) than the AT pairing, which has two hydrogen bonds.

Convergence

Convergence arises when nature solves the same challenge more than once through adaptive evolution of superficially similar structures, such as the wings of birds and insects, or the development of "anti-freeze" proteins in the blood of fish in both the Arctic and Antarctic Oceans.

Crossing-over

The exchange of corresponding regions between maternal and paternal chromosomes.Crossing-over results in genetic recombination.

CRS

See Cambridge Reference Sequence.

Cytosine

The "C" in ATGC, the four bases found in DNA."C" is short for cytosine, a base that bonds with Guanine (G) in double stranded DNA.

Displacement (D) loop region

In mitochondrial DNA, the D-loop is a short triple-stranded region that contains regulatory sequences.The D-loop contains severalhypervariable regions that have relatively higher rate of mutation compared to the coding region of mtDNA.Transcription (DNA to RNA) originates from two closely spaced promoters located in the D loop region.The replication (i.e., duplication of DNA) of both strands is unidirectional and starts at specific "origins of replication" in the D loop.

DNA (deoxyribonucleic acid)

The double helix-shaped molecule that holds an organism's genetic information.The DNA in each cell contains over 3 billion base pairs coding the approximately 25,000 genes that make up the human genome. DNA is composed of sugars, phosphates, and four nucleotide bases: adenine, guanine, cytosine, and thymine (A, G, C, T). The bases bind together in specific pairs - A:T and G:C.

DNA Letters

The DNA molecule is composed of a string of four chemicals called adenine, cytosine, guanine and thymine, normally abbreviated to A, C, G and T, respectively.

DNA Sequence

The order or arrangement of the DNA letters (A, T, C & G) making up the DNA molecule.

DNA sequencing

Laboratory procedure for determining the exact order of bases (ATCG) in a strand of DNA.In "bi-directional sequencing" the sequence of both complementary strands is obtained.

DNA

Short for DeoxyriboNucleic Acid. The genetic material carried by all animals and plants that allows transmission of characteristics from one generation to the next.

Enzyme

A protein that catalyzes a specific chemical reaction.

Gene

The basic unit of inheritance.A gene is a sub-unit of DNA in a particular position on a particular chromosome that contains the genetic code to make a particular protein.

Genealogy

 The study of lines of descent. Alternatively, a line of descent traced continuously from an ancestor.

Generation time

The number of years between the birth of parents and the birth of their children.

Genetic Ancestry

Line of descent supported by genetic evidence.

Genetic Marker

Any part of the DNA molecule that expresses variability within a population and that can be used for analysis of that population.

Genetics

The study of heredity and the variation of inherited characteristics or the genetic properties or features of an organism.More simply, the study of how particular traits are transmitted from parents to offspring.

Genetic drift

The occurrence of changes in gene frequency brought about by chance rather than by selection.

Genogram

Diagram that depicts the phylogenetic relationship of mitochondrial haplogroups (the line connecting the circles) and the relative size of the populations (the area of the labeled circles).

Genome

The entire complement of genetic material in a nucleus (23 pairs of chromosomes) or an organelle (mitochondrial DNA). The mitochondrial genome is 16,569 bases long, circular and resides within the mitochondrion.

Genotype

The set of genes of an individual.

Guanine

The "G" in A, T, G & C, the four bases found in DNA."G" is short for guanine, a base that bonds with Cytosine (C) in double stranded DNA.

H

Haplogroup

A group of haplotypes that share common ancestry defined by shared sequence.Haplogroups are the main branches of the human genealogical tree and reflect early human migrations. A haplogroup contains all the direct descendants of a single person (man or woman) who passed on a specific genetic marker or mutation.

Haplotype

Different combinations of polymorphisms are known as haplotypes.A set of closely linked alleles (genes or DNA polymorphisms) inherited as a unit.A contraction of the phrase "haploid genotype."

Heredity

The passing on of physical or mental characteristics genetically from one generation to another.

Heteroplasmy

The presence of two or more mtDNA genotypes in a single DNA sample.

Homoplasmy

Having all copies of mtDNA the same within a cell or organism (compare heteroplasmy).Not to be confused with homoplasy, which means something entirely different!

Homoplasy

In mitochondrial or chromosomal DNA, a situation in which the same polymorphism arises independently in two or more haplogroups.Homoplastic polymorphisms are more likely in regions of high mutation rate and limit the "informativeness" of the polymorphism.In a broader biological context, homoplasy refers to similar features that are NOT derived form a common ancestral feature, and have thus arisen from parallelism, convergence, or chance.

Human Migration

The movement of historic populations of Man out of Africa and across the continents of the world.

Hypervariable region

See D-loop, above.

Identity by descent (IBD)

Alleles that are identical because they have both been inherited from a common ancestor, as opposed to identity by state (IBS).

Identity by state (IBS)

Coincidental possession of alleles that appear to be identical but have not been proved to be of common descent.

Locus

The position of a particular gene on a chromosome.

Marker

A physical location (locus) on the chromosome.

Matrilineal

Passed down exclusively from the mother.

Meiosis

A special type of cell division that occurs when gametes (spermatozoa and eggs) are formed.Each gamete contains just one version of each gene.

Metabolism

The chemical processes occurring within an organism that are necessary for the maintenance of life.

Migration Routes

The lines of travel taken by our ancestors as they migrated out of Africa and colonized the other continents.

Mitochondria

Plural of mitochondrion. Mitochondria are the "powerhouses of the cell".Their function is to break down sugars and release energy for use by the cell.They have their own circular genome.

Mitochondrial DNA or mtDNA

The circular, 16,569 base pair long genome of the mitochondrion.It encodes 13 protein coding genes, two ribosomal RNAs and 22 transfer RNAs.Because the sperm cell does not contribute any mitochondria to the fertilized egg, all of the mitochondria in both male and female offspring are derived from the mother.It is ideal for tracing recent human history, such as the emergence of ethnically distinct lineages or haplogroups,because of its relatively high mutation rate and lack of recombination.

Mitochondrial Eve

Also known as African Eve. The human female who lived approximately 150,000 to 200,000 years ago and from whom everyone on this planet is descended through the maternal line.More about Eve.

MitoMap

An online human mitochondrial genome database (www.mitomap.org)

Molecular clock

The clock-like regularity of the change of a gene over geological time.Different genetic regions may have quite different rates of change.

MRCA

Most recent common ancestor

mtDNA

See Mitochondrial DNA.

Mutation

An inheritable alteration in the genetic material.At the level of the whole organism, mutations can be divided into germ line and somatic types. Those that occur in the cells that make spermatozoa or eggs (germ cells) can be passed on to the next generation. Mutations that occur in somatic (non-germ) cells and are not transmitted to progeny.Somatic mutations are common in cancer tissue. A non- synonymous ormissense mutation results in an amino acid change in a protein.A synonymous or silent mutation replace one codon with another that encodes the same amino acid.

Mutation rate

The rate at which changes occur in DNA sequence.Regions coding for proteins have a lower mutation rate than non-coding DNA since they may alter protein structure and are thus selected against.As an example, say the mutation rate of the coding region of mtDNA is approximately 1.7% per million years.Thus if a population of mtDNAs has an average difference of 0.3% within the coding region, one can estimate that they began to diverge from a common ancestor around 175,000 years ago (i.e., 0.3/1.7 million years ago).Because the mutation rate of the D-loop region in mtDNA is faster than the rate for the coding region, it will take less time to reach the same level of population diversity for this region.Because of this high mutation rate, reliance on the hypervariable D-loop region to establish phylogenetic networks is limited by the effects of saturation and homoplasy.

Non-synonymous mutation

A mutation in DNA that alters the amino acid composition of a protein.

Nucleotide

A nucleotide is formed by adding a sugar unit and a phosphate to a base.Nucleotide triphosphates are used by the cell to form the nucleic acid polymers RNA and DNA.

Nucleus

The membrane bound organelle containing the chromosomes.

OMIM - Online Mendelian Inheritance in Man

A central database of human genes involved in disease.

Organelle

A structure within a cell, such as a mitochondrion, that performs a specific function.Organelle = "little organ".

Organism

An individual animal, plant or single-celled life form.

Parallelism

An evolutionary event where two identical changes occur independently.

PCR - Polymerase Chain Reaction

A biochemical technique that allows the specific amplification (production of multiple copies) of extremely small amounts of particular DNA fragments using DNA polymerase and specific primers.

Phylogeny

The inferred lines of descent from a common ancestor.The etymology of the word is interesting: phylo- means "tribe" or "clan"; -geny means "origins".

Polymorphism

The simultaneous occurrence of two or more versions of a gene in a population.In mitochondrial DNA, it usually refers to different bases at a particular position, such as A750G.The frequency of the rarest form of the polymorphism is higher than can be maintained by recurrent mutation.

Primer

A short DNA molecule used for PCR and for sequencing.

Protein

Proteins are made up of amino acids - they are the main building blocks of our cells.

Purine

Adenine and Guanine are purine bases; thymine and cytosine are pyrimidine bases.Purines consist of a six-membered and a five-membered nitrogen-containing ring, fused together. Pyridmidines have only a six-membered nitrogen-containing ring.

Pyrimidine

Thymine and cytosine are pyrimidine bases.

Recombination

The reshuffling of the genes in a fertilized egg as a result of crossing-over and re-assortment of the chromosomes during meiosis (ie, during the formation of the sperm and egg).Mitochondrial DNA does not recombine.

Replication

The process by which the DNA double helix makes an exact copy of itself or of a fragment. It uses the DNA as a template for the synthesis of new DNA strands.

Root Node

The original sequence of any specific clan mother or father.

Sequence

See DNA Sequence.

Sequencing

The determination of the order of the four DNA letters within the DNA molecule. Once the DNA is extracted and purified from a cell sample, it is amplified and the sequence determined using a DNA sequencer.

Sex chromosomes

The X and Y chromosomes. Normally males have one X and one Y and females have two X's. Sex chromossomes make up the 23rd pair, different from the other 22 pairs that are the autosomal DNA.

Silent Mutation

See synonymous mutation

SNP - Single Nucleotide Polymorphism

Changes in the DNA that happen when a single nucleotide (A, T, G, or C) in the genome sequence is altered. A person has many SNP's that together create a unique DNA pattern for that individual.

Synonymous mutation

A change in DNA sequence that does not result in a change in protein sequence.Also called silent mutations, these are usually "invisible" to selective pressure since they don't alter protein sequence.

Thymine

The "T" in ATGC, the four bases found in DNA."T" is short for thymine, a base that bonds with adenine (A) in double stranded DNA.

TMRCA

Time to the Most Recent Common Ancestor.

Transmission event

The passage of genes from one generation to the next.

Tribes

Traditionally used to describe a large number of people with the same culture and dialect.

X

X chromosome

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.

Z

Zygote

A fertilized egg.