Glossary of Terms
It is very difficult to present information related to studies
in cancer genetics without using
many words that are unfamiliar to most folks. The following is a
list of definitions of some of the technical terms that are used
on this Website. We hope that this information will make it easier
to understand the material that we are presenting.
One of the variant forms of a gene at a particular locus, or location,
on a chromosome. Different
alleles produce variation in inherited
characteristics such as hair color or blood type. In an individual,
one form of the allele (the dominant
one) may be expressed more than another form (the recessive
A low red blood cell count. Red
cells are the cells which carry oxygen from the lungs through the
bloodstream to other organs throughout the body.
A disease in which the bone marrow fails to make all three types
of cells which it normally produces.
These include red cells, white
cells and platelets. Aplastic
anemia has many causes including exposure to toxic chemicals, certain
unusual infections and rare genetic abnormalities.
A pattern of Mendelian
inheritance whereby an affected individual possesses one copy
of a mutant allele and one normal
allele. (In contrast, recessive
diseases require that the individual have two copies of the mutant
allele.) Individuals with autosomal dominant diseases have a 50-50
chance of passing the mutant allele and hence the disorder onto
their children. Examples of autosomal dominant diseases include
Huntington's disease, neurofibromatosis, and polycystic kidney disease.
Any chromosome other than
a sex chromosome. Humans
have 22 pairs of autosomes.
Diseases in which abnormal cells
divide and grow unchecked. Cancer can spread from its original site
to other parts of the body and can also be fatal if not treated
Any of the various types of cancerous tumors that form in the
epithelial tissues, the tissue forming the outer layer of the body
surface and lining the digestive tract and other hollow structures.
Examples of this kind of cancer
include, breast, lung, and prostate cancer.
An individual who possesses one copy of a mutant allele
that causes disease only when two copies are present. Although carriers
not affected by the disease, two carriers can produce a child who
has the disease.
The basic unit of any living organism. It is a small, watery, compartment
filled with chemicals and a complete copy of the organism's genome
or DNA. The DNA is located in the
nucleus of the cell.
One of the threadlike "packages" of genes
and other DNA in the nucleus
of a cell. Different kinds of organisms have different numbers of
chromosomes. Humans have
23 pairs of chromosomes, 46 in all: 44 autosomes
and two sex chromosomes. Each parent contributes one chromosome
to each pair, so children get half of their chromosomes from their
mothers and half from their fathers.
To make copies in the laboratory of a specific piece of DNA,
usually a gene. When geneticists
speak of cloning, they do not mean the process of making genetically
identical copies of an entire organism.
A cohort is a group of people who participate in a research study
in which participants' health is monitored over time.
Any trait or condition that exists from birth.
A particular kind of mutation:
loss of a piece of DNA from a chromosome.
Deletion of a gene or part of a
gene can lead to a disease or abnormality.
The chemical inside the nucleus
of a cell that carries the genetic instructions for making living
A gene that almost always results
in a specific physical characteristic, for example, a disease, even
though the patient's genome possesses
only one copy. With a dominant gene, the chance of passing on the
gene (and therefore the disease) to children is 50-50 in each pregnancy.
A protein that encourages a biochemical reaction, usually speeding
it up. Organisms could not function if they had no enzymes.
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.
A short-term educational counseling process for individuals and
families who have a genetic disease or who are at risk of such a
disease. Genetic counseling provides patients with information about
their condition and helps them make informed decisions about their
All the DNA contained in an organism
or a cell, which includes both
the chromosomes within the
nucleus and the DNA in mitochondria.
Inherited material that comes
from the eggs or sperm and is passed on to offspring.
Possessing two different forms of a particular gene,
one inherited from each parent.
Possessing two identical forms of a particular gene,
one inherited from each parent.
Human Genome Project
An international research project to map each human gene
and to completely sequence all human DNA.
Transmitted through genes from
parents to offspring (children).
The set of chromosomes possessed
by an individual, including the number of chromosomes and any abnormalities
in individual chromosomes. The term is also used to refer to a photograph
of an individual's chromosomes.
Cancer of the developing blood
cells in the bone marrow. Leukemia
leads to overproduction of white
blood cells (leukocytes); symptoms usually include anemia,
fever, enlarged liver, spleen, and/or lymph nodes.
A small white blood cell
that plays a major role in defending the body against disease. There
are two main types of lymphocytes: B cells, which make antibodies
that attack bacteria and toxins, and T cells, which attack body
cells themselves when they have
been taken over by viruses or become cancerous.
Manner in which genes and traits
are passed from parents to children. Examples of Mendelian inheritance
include autosomal dominant,
autosomal recessive, and sex-linked
The organelles which generate energy for the cell.
A permanent structural alteration in DNA.
In most cases, DNA changes either have no effect at all or they
cause harm (or disease), but occasionally a mutation can improve
an organism's chance of surviving and passing the beneficial change
on to its descendants.
Neutrophils are a particular kind of white
blood cell. They are a very important part of the body’s defense
against bacterial infection. If the neutrophil count in the blood
is lower than normal, the patient is said to have "Neutropenia."
The central cell structure that
houses the chromosomes and
A simplified diagram of a family's genealogy that shows family
members' relationships to each other and how a particular trait
or disease has been inherited.
Platelets are the cells which
help the blood to clot. They are made in the bone marrow, and circulate
through the body in the bloodstream, where they are carried to sites
A common (frequent) variation in the sequence of DNA
A large complex molecule made up of one or more chains of amino
acids. Proteins perform a wide variety of activities in the cell.
A genetic disorder that appears only in patients who have received
two copies of a mutant gene, one
from each parent.
One of the two chromosomes
that specify an organism's genetic sex. Humans have two kinds of
sex chromosomes, one called X and the other Y. Normal females possess
two X chromosomes and normal males one X and one Y.
Located on the X chromosome.
Sex-linked (or x-linked) diseases are generally seen only in males.
All body cells, except the reproductive
(or germ) cells.
The group or recognizable pattern of symptoms or abnormalities
that indicate a particular trait or disease.
The technical term for a low platelet
White cells are part of the body’s immune system. They play an
important role in fighting off infection and cancer.
There are several different varieties of white cells, including
eosinophils and basophils.
*Modified from the Glossary of Genetic Terms published
by the National Human Genome Research Institute. See the following
Webpage for more information: http://www.genome.gov/glossary.cfm