Glossary

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Cell The smallest unit of living matter that can operate independently.

Chromosomes are bundles of tightly coiled DNA. Humans have 23 paired chromosomes (22 pairs of autosomes and a single pair of sex chromosomes). A single chromosome of each pair is passed from each parent to child.  A structure found in the nucleus of a cell that contains genetic material.

Cambridge Reference Sequence (CRS)
The mitochondrial DNA first sequenced in 1981 which is used as a basis for comparison with mtDNA test results.

Catalyst
A substance which starts or speeds up a chemical reaction without being affected by that reaction.

Coding region
A region of DNA which contains genes.

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.

Combined DNA Index System (CODIS)
The CODIS system uses marker locations in the autosomal DNA. CODIS test results are maintained in an FBI database which is used to identify people and solve crimes.

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 lineages changing over time to resemble one another.

Cross-over
See recombination.

Cytosine
The "C" of the four bases that make up DNA. The other bases are adenine (A), guanine (G), and thymine (T). Cytosine always pairs with guanine.

Darwin, Charles His work became the foundation of modern evolutionary theory. Charles Darwin's 1859 book The Origin of Species promoted a theory of evolution by natural selection and challenged Victorian-era ideas about the role of humans in the universe. Darwin's theories were based on a constantly evolving natural world and held that each generation of a species had to compete for survival. Survivors held some natural advantages over their unfortunate relatives and passed those characteristics on to their progeny, thus over-representing these favored genetic types in the next generation. Darwin also advanced the idea that species were descended from a common ancestor. Darwin's work became the foundation of modern evolutionary theory.

DNA (Deoxyribonucleic Acid): The double helix-shaped molecule that holds an organism's genetic information. 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 (see detailed entry below).  A chemical consisting of a sequence of hundreds of millions of nucleotides found in the nuclei of cells. It contains the genetic information about an individual and is shaped like a double-stranded helix.

DNA amplification
The production of many DNA copies from one or a few copies or fragments.

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.

DNA Y-chromosome Segment (DYS)
The "name" of a marker on the Y-chromosome. It is assigned based on a nomenclature system controlled by the HUGO Gene Nomenclature Committee, which assigns DYS numbers to newly discovered markers.

Double Helix: The double helix-shaped molecule holds an organism's genetic information.  The twisted shape of DNA, when its two strands bond together, much like a spiral staircase or twisted ladder. The stairway's railings are composed of sugars and phosphates. Its sides contain the patterned base pairs: A, T, C, and G. When a cell divides for reproduction, the helix unwinds and splits down the middle like a zipper in order to copy itself.

DYS
D = DNA: Y = Chromosome; S = Single copy sequence. The DYS numbering scheme (e.g. DYS388, DYS390) for the Y-STR haplotype markers are controlled and administered by an international standards body called HUGO - Human Gene Nomenclature Committee - based at University College, London.

Enzyme
A protein that facilitates a specific chemical reaction by working as a catalyst.

Exact match
Two individuals with exactly the same results for all markers or regions compared.

Family Tree DNA Time Predictor (FTDNATiPTM)
A program used to calculate estimates of Time to the Most Recent Common Ancestor (TMRCA). It is the world's first calculator that incorporates mutation rates specific to each marker. This greatly increases the power and precision of estimates.

FOXP2: The first gene to be linked to language production, and the key to the development of brain regions associated with speech. FOXP2's discovery suggests that the development of language may be tied to a genetic mutation that could have occurred some 50,000 years ago, in the same time range as the first great human migrations out of Africa.

 Gene the functional and physical unit of heredity passed from parent to offspring.  A segment of DNA which contains the genetic code to make a certain protein or part of a protein.

Genes: Segments of DNA that are the basic functional units of heredity. Genes are determined by an ordered sequence of chemical bases found in a unique position on a specific chromosome. Their "blueprint" guides protein production, which determines how different cells in the body function. Inherited genes also control an animal's unique set of physical traits.

Genealogical Data Communication (GEDCOM)
A type of file format used by genealogical software to make your family tree. You can upload your GEDCOM file to your Family Tree DNA personal page as well as Ysearch or mitosearch. Learn more about GEDCOM here

Genealogy
The study of family history.

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. At Family Tree DNA we use 25 years.

Genetic cousins
Individuals whose Y-DNA or mtDNA test results match one another.

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).

Genetics
The study of genes and heredity; the study of DNA.

Genetic Marker: Random mutations in the DNA sequence which act as genetic milestones. Once markers have been identified they can be traced back in time to their origin—the most recent common ancestor of everyone who carries the marker.

Genome: The total DNA sequence that serves as an instruction manual for all proteins created in our body. Two copies of the genome are found inside each of our cells.  The entire complement of genetic material in a chromosome set. The human genome is composed of 46 chromosomes, with a total of 3 billion base pairs.

Genotype the actual alleles present in an individual.  Haplotype is a genotype of genetically linked loci that are inherited in a block as a single unit.  Modal Haplotype (MH) Definition: any person who exactly matches the alleles found to be most common (Modal) among the descendants of a person. A person who matches 20 alleles while being 1 allele off in only 1 locus will be considered to be in the haplogroup, rather than in the family haplotype.

Glacial maximum
The scientific term for the peak of an ice age.

Guanine
The "G" of the four bases that make up DNA. The other bases are adenine (A), cytosine (C), and thymine (T). Guanine always pairs with cytosine.

Haplogroup: Branches on the tree of early human migrations and genetic evolution. Haplogroups are defined by genetic mutations or "markers" found in Y chromosome and mtDNA testing. These markers link the members of a haplogroup back to the marker's first appearance in the group's most recent common ancestor. Haplogroups often have a geographic relation.  Haplogroups are large groups that can be used to define genetic populations and are often geographically orientated. For example, when the Y-chromosome is tested, many males who live along the western coasts of Europe belong to Haplogroup R1b (used to be called HG1), which belies the historical movement of males along that coast.

The Y-chromosome haplogroup of an individual is not defined by their haplotype (because haplotypes are determined by STR markers). Instead, they are determined by SNP's (single nucleotide polymorphisms) where a single base changes e.g. from A to G. These happen so rarely as to be considered unique.

However, there is a strong correlation between haplogroups and haplotypes so given any particular haplotype, it may be possible to correctly determine the haplogroup without any further tests (see Masterclass).

It is important to note that even though female and male haplogroups may have the same letters, their definitions are different.

Haplotype
Your Y-DNA haplotype is a set of 21 numbers (if using 21 STR markers), each number representing your allele at a given STR marker. Two or more haplotypes may be compared as a check for a genetic relationship.  Two individuals that match exactly on all markers have the same haplotype.

There are many haplotypes to be found from many different populations around the globe at www.yhrd.org that may be used to compare haplotypes. Also, the Ybase database can accept genealogical as well as haplotype data.

Haplotype diversity
A measure of the uniqueness of a particular haplotype in a given population.


Heredity: The total sum of genetic information that humans pass on from generation to generation.  The transmission of genetic material from parents to offspring.

Human Genome Organization (HUGO)
The entity to which, among other things, scientists submit new markers for DYS number assignment.

Hypervariable Region (HVR)
One of two regions commonly used in mitochondrial DNA tests which does not code for any known function.

Junk DNA
Stretches of DNA that do not code for genes, also called non-coding DNA. Most of the genome consists of non-coding DNA, and was therefore long thought to be 'junk.' Scientists have found that in addition to containing markers that are helpful for genetic genealogy, parts of these non-coding regions have regulatory and other functions.

Locus (pl. loci) 

Loci  The plural of locus, or marker. Locus and loci are Latin words for location(s).

Locus (plural-loci)  Latin for place. A specific spot in the genome.  A variable locus will have several possible alleles.  See marker. 

 Marker
Also called a Locus (pl. loci). A gene of a known location on a chromosome. See STR marker. The DNA Heritage Y-DNA test uses 21 STR markers.  Family Tree DNA offers 3 levels of Y-DNA testing: 12-marker,  37-marker, and 67-marker.

Meiosis
The stage in which sperm and egg cells are formed. It is during this process that the autosomal chromosomes recombine and mutations occur.

Melanin/Vitamin D/Skin Color: Melanin, the skin's brown pigment, is a natural sunscreen that protects tropical peoples from the many harmful effects of ultraviolet (UV) rays. But when UV rays penetrate the skin they also produce beneficial vitamin D, so some exposure to them is necessary. This delicate balancing act explains why the peoples that migrated to darker, colder climes also developed lighter skin color. As people moved to areas with lower UV levels, their skin lightened so that UV rays could penetrate and produce essential vitamin D. In some cases a third factor intervened. Coastal peoples who eat diets rich in seafood enjoy an alternate source of vitamin D. That means that some Arctic peoples, for example, can afford to remain dark-skinned even in low UV climes.

Microsatellite
See short tandem repeat.

Mitochondria: A remnant of an ancient parasitic bacteria that now helps to produce energy inside the cell. A mitochondrion has its own genome, present in only one copy, which does not recombine in reproduction. This genetic consistency makes mitochondrial DNA a very important tool in tracking genetic histories.  A specific organelle in the cell that helps it to produce energy.

Mitochondrial DNA or mtDNA: Genetic material found in the mitochondria. It is passed from females to their offspring without recombining, and thus is an important tool for geneticists.  It is passed down from females to both sons and daughters, but sons do not pass down their mother's mtDNA to their children.

Modal comes from the statistical term Mode, which means the value at which an absolute or maximum occurs in the frequency distribution of the variant.

Modal haplotype
The most common result for each marker tested in a group of results. See also: ancestral signature.

Modal Associations of the R Haplotypes



Most Recent Common Ancestor (MRCA)
The ancestor shared most recently between two individuals.

Mutation
A heritable change that occurs in genetic material. It may lead to a different number of repeats of a certain sequence or a change in one of the bases in a sequence.

Mutation rate
The frequency with which random mutations occur.

Nucleotide: A DNA building block which contains a base, or half of a "staircase step," and sugars and phosphates which form the "railing." Nucleotides join together to form DNA's distinctive double helix shape.  A piece of DNA that contains one base, one phosphate group, and one sugar unit. Thousands of nucleotides joined in sequence make a molecule of DNA.

Nucleus: The part of the cell in which chromosomes reside.  The membrane-bound organelle containing the chromosomes.

Pherogram
For STRs, a plot which shows the length of a fragment of DNA. This allows its allele value to be measured.

Phylogeny: The evolutionary development of a species. Phylogeny is sometimes represented as a tree that shows the natural relations and development of all species.

Point Mutation a change in a single base pair.

Population genetics: The study of genetic variation in a species.

Proteins: Linear sequences of amino acids that are the building blocks of cells. Each protein has a specific function that is determined by the "blueprint" stored in DNA.

Phylogenetic tree
See Y-DNA phylogenetic tree.

Polymerase
The enzyme that starts the process of making nucleic acids or assembling RNA or DNA.

Polymerase Chain Reaction (PCR)
A technique allowing the production of multiple copies of extremely small amounts of DNA fragments using DNA polymerase and specific primers.

Polymorphism
See mutation.

Primer
A short DNA sequence used in the polymerase chain reaction to initiate DNA synthesis at a particular location.

Protein
The main building block of our cells. Each one has a specific function.

 Recombination: The process by which each parent contributes half of an offspring's DNA, creating an entirely new genetic identity. This process mixes genetic signals, so that nonrecombining DNA, passed intact through the generations, is most important to population genetics.  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.

Replication: The process by which two DNA strands separate, with each helping to duplicate a new strand. During reproduction, the DNA double helix unwinds and duplicates itself to pass on genetic information to the next generation. Because bases always form established pairs (AT and CG), the sequence of bases on each strand will attract a corresponding match of new bases. Only occasional errors occur—about one for every billion base-pair replications.  See DNA replication.

RNA (Ribonucleic Acid): Transfers the genetic "blueprint" that is stored in DNA during protein production. RNA has a single-stranded linear structure and a slightly different chemical composition from DNA.

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.

Sequencing: Determines the order of nucleotides for any particular DNA segment or gene. The order of a DNA string's base pairs determines which proteins are produced, and thus the function of a particular cell.  See DNA sequencing.

Sex chromosome
The X- or Y-chromosome. Normally males have one X and one Y and females have two Xs.

Sexual Selection: Special form of natural selection based on an organism's ability to mate. Some animals possess characteristics that are more attractive to potential mates, such as the distinctive plumage of some male birds. Individuals with such characteristics mate at higher rates than those without, ensuring more next generation offspring will inherit the desirable trait. As generations procreate the desirable trait becomes increasingly common, further boosting the sexual disadvantage for individuals who lack the desired trait. The effect can be particularly dramatic when one individual controls mating with a large number of potential partners.

Short Tandem Repeat (STR)
A short DNA motif (pattern) repeated in tandem. ATGC repeated eleven times would give the marker a value or allele of 11.


Single Nucleotide Polymorphism: Small, infrequent changes which help to create an individual's own unique DNA pattern. When a single nucleotide (A, T, G, or C) in the genome sequence is altered during DNA replication, due to a tiny "spelling mistake," the genome sequence is altered.  A person has many SNPs that together create a unique DNA pattern for that individual.

STR (Short Tandem Repeat) A region of repetitive DNA with short units of repetition (2 to 6 basis).

Surname
A last name or family name traditionally passed down from father to son.

Thymine
The "T" of the four bases that make up DNA. The other bases are adenine (A), cytosine (C), and guanine (G). Thymine always pairs with adenine.

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.

TMRCA this term used by population geneticists indicates the Time to the Most Recent Common Ancestor shared with another person.

Trait: The physical characteristics, like eye color or nose shape, which are determined by inherited genes.

Transmission event
The passage of genetic material from one generation to the next.

Unique Event Polymorphism (UEP)
See single nucleotide polymorphism.

Western Atlantic Modal Haplotype (WAMH)
The most common Y-DNA haplotypes found in Europe’s most common Y-DNA haplogroup, R1b.

 X and Y Chromosomes: Chromosomes which determine sex. Females have two X chromosomes while males have one X and one Y. When chromosomes pair, the mismatched Y determines male gender. Because of the mismatch, part of the Y chromosome does not recombine with the X during reproduction. The nonrecombining part of the Y chromosome contains a sequence of DNA passed intact from males to their sons through the generations, giving population geneticists a useful tool for studying human history.  The Y-chromosome passes down from father to son. Females do not receive it. The fact that the Y-chromosome goes down the paternal line makes it valuable for genealogy studies, since it typically follows a surname line.

Y-DNA non-recombining DNA determines whether a child will be a male or female. Y-DNA passes from father to son almost unaltered for long periods of time.

Y-DNA phylogenetic tree
A graphic representation of the Y-DNA haplogroups according to the YCC classification. Haplogroup names and major clades are labeled and mutation names are given along the branches of the trees.

Y-chromosome
The sex chromosome that instructs a foetus to grow into a baby boy. It is passed down from generation to generation only through the male line i.e. from father to son, father to son, etc. It is approx. 60 million base-pairs long.