Y-DNA Glossary
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Y-DNA Analysis
Glossary of Terms

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Allele: One of the variant forms of a gene at a particular locus, or location, on a chromosome. Different alleles produce variation in inherited characteristics. For STR markers, each allele is the number of repeats of the short base sequence. A list of marker labels and their associated allele values constitutes an individualís haplotype.

Anthropological Time Frame: A time frame that at predates surnames for most people. It ranges roughly between one thousand and one hundred thousand years ago. The Y-DNA haplogroup tree traces SNP mutations over anthropological time.

One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Chromosomes are normally found in pairs; human beings typically have 23 pairs of chromosomes.

Clade: From the Greek word klados, meaning branch. A clade on the Y chromosome tree is also called a haplogroup.

Deep Ancestry: Ancestry in an anthropological time frame of over 1000 to tens of thousands of years ago that predates recorded history and surnames for most people. The Y-DNA haplogroup tree traces SNP mutations to show deep ancestry.

DNA (DeoxyriboNucleic Acid): The chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.

DNA sequencing: The determination of the precise sequence of nucleotides in a sample of DNA.

DYS#: D=DNA, Y=Y chromosome, S=a unique DNA segment. A label for genetic markers on the Y chromosome. Each marker is designated by a number, according to international conventions. At present, virtually all the DYS designations are given to STR markers (a class often used in genetic genealogy).

False Paternity: See Hidden Paternity (separate page)

Gene: The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.

Genealogical Time Frame: A time frame within the last 500 up to 1000 years since the adoption of surnames and written family records. An individual's haplotype is useful within this time frame and is compared to others to help identify branches within a family.

Genetic Genealogy: The tracing of human lineage within the time frame of historical records through DNA testing and comparison of haplotypes.

Genome: All the DNA contained in an organism or a cell, which includes both the chromosomes within the nucleus and the DNA in mitochondria.

Haplotype: The result received for a Y-DNA test is a string of allele values called a Haplotype. Grouping the results by haplotype helps identify family branches.

Haplogroup: A Haplogroup identifies the person's major population group and provides information about the ancient origin of the male line.

Hidden Paternity: A break in one's male ancestral lineage in which a person believed to the father of a particular individual is not the biological father. (Reasons and Probabilities)

Human Genome Project: An international research project to map each human gene and to completely sequence human DNA, i.e. to sequence the entire human genome, the complete complement of all genetic material in the human species. The human genome sequencing was completed in 2003.

Locus: A point in the genome, identified by a marker, which can be mapped by some means. It does not necessarily correspond to a gene. A single gene may have several loci within it (each defined by different markers) and these markers may be separated in genetic or physical mapping experiments. In such cases, it is useful to define these different loci, but normally the gene name should be used to designate the gene itself, as this usually will convey the most information.

Marker: Also known as a genetic marker, a marker is a segment of DNA with an identifiable physical location on a chromosome whose inheritance can be followed. A marker can be a gene, or it can be some section of DNA with no known function. Each marker has a name assigned to it by the scientific community, such as DYS#391, DYS#439 or GATA H4. The scientists classify these markers as Short Tandem Repeats (STR) because at each of these marker locations a short DNA code repeats itself. The result for a marker is the number of times the code repeats at that location and is called the allele value.

Mutation: A permanent structural alteration or change in the DNA sequence. Mutations in the sperm or egg are called germline mutations. Germline mutations in the Y chromosome of the male are passed on to all of his male-line descendants. Mutations that occur after conception are called somatic mutations; these mutations may be found in different tissues of the body and they are not passed on to offspring.

Non-paternal Event (NPE): An event which caused a break in one's male ancestral lineage, also known as Hidden Paternity.

NRY: Non-recombining Y, the large central portion of the Y chromosome that does not exchange material with the X chromosome.

Nucleotide: A sub-unit of DNA made of a molecule of sugar, a molecule of phosphoric acid, and a molecule called a base.

Paternal Line of Descent. A direct line of descent from ancestral father to son to son to son along an all male line which is traced through Y-DNA.

Phylogenetic Tree: A diagram showing evolutionary lineages of organisms.

Polymorphism: A variation in the sequence of genetic information on a segment of DNA.

Short Tandem Repeats (STR): A genetic marker consisting of multiple copies of an identical DNA sequence arranged in direct succession in a particular region of a chromosome. Occasionally, one will mutate by the gain or loss of one repeat.

Single Nucleotide Polymorphism (SNP which is pronounced 'snip') Variation in the nucleotide allele at a certain nucleotide position in the human genome. When the change occurs it is called a polymorphism, and polymorphisms accumulate over time. A polymorphism can be very common (found in a significant fraction of global or localized populations) or very rare (found in a single individual). Common variations are used to track the evolution of the human genome over time (population genetics) and can be graphically represented in a haplogroup or phylogenetic tree.

SNP: A Single Nucleotide Polymorphism (see above)

X chromosome
: One of two types of sex-determining chromosomes, the other being the Y chromosome. When two X chromosomes, one from each parent, are paired with each other in a fertilized egg cell, the resulting child will be female. If the fertilized egg cell contains both an X and a Y chromosome, the resulting child will be male. The X chromosomes become subject to cross-over effects during subsequent egg cell creation in the female offspring, and certain alleles in both these X chromosomes can randomly swap positions in the next generations making it very difficult to track a particular X chromosome over more than a couple of generations. Determining a common ancestor for an X chromosome is very difficult beyond a couple of generations; therefore, the X chromosome is not a very useful tool for genetic genealogy purposes.

Y chromosome: The Y chromosome is the chromosome that makes a person a male and can be passed by a male only to his sons. It differs from all other chromosomes in that the majority of the chromosome is unique and does not recombine during cell division (see NRY or non-combining Y). This means the historical pattern of mutations can easily be studied.

Y-DNA: The DNA in the Y chromosome that can be passed by a male only to his sons. This DNA can be tested to determine both haplotype and haplogroup of the individual.

Source: Many of these definitions were adapted from the Glossary of Genetic Terms published by the International Society of Genetic Genealogists.

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Last Revised: 02 Jan 2015

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