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.
Chromosome: 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
DNA (DeoxyriboNucleic Acid): The chemical inside the nucleus of a cell that
carries the genetic instructions for making living
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
and most genes contain the information for making a specific
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.
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
Haplotype: The result
received for a Y-DNA test is a string of
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
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
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
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
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.
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
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.