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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 one).


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.

Aplastic Anemia

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.

Autosomal Dominant

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 adequately.


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 organisms.

Dominant Gene

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.

Genetic Counseling

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 medical care.


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

Germ Line

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.

Mendelian inheritance

Manner in which genes and traits are passed from parents to children. Examples of Mendelian inheritance include autosomal dominant, autosomal recessive, and sex-linked genes.


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 DNA.


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 of injury.


A common (frequent) variation in the sequence of DNA among individuals.


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.

Sex Chromosome

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.

Sex Linked

Located on the X chromosome. Sex-linked (or x-linked) diseases are generally seen only in males.

Somatic Cells

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 count.

White Cell

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 neutrophils, lymphocytes, 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:


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