Glossary

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Acquired mutations:

gene changes that arise within individual cells and accumulate throughout a person's lifetime; also called somatic mutations. (See Hereditary mutation.)

Alleles:

variant forms of the same gene. Different alleles produce variations in inherited characteristics such as eye color or blood type.

Alzheimer's disease:

a disease that causes memory loss, personality changes, dementia and, ultimately, death. Not all cases are inherited, but genes have been found for familial forms of Alzheimer's disease.

Amino acid:

any of a class of 20 molecules that combine to form proteins in living things.

Amyotrophic lateral sclerosis:

an inherited, fatal degenerative nerve disorder; also known as Lou Gehrig's disease.

Autosome:

any of the non-sex-determining chromosomes. Human cells have 22 pairs of autosomes.

Base pairs:

the two complementary, nitrogen-rich molecules held together by weak chemical bonds. Two strands of DNA are held together in the shape of a double helix by the bonds between their base pairs. (See Chemical base.)

BRCA1:

a gene that normally helps to restrain cell growth.

BRCA1 breast cancer susceptibility gene:

a mutated version of BRCA1, which predisposes a person toward developing breast cancer.

Carrier:

a person who has a recessive mutated gene, together with its normal allele. Carriers do not usually develop disease but can pass the mutated gene on to their children.

Carrier testing:

testing to identify individuals who carry disease-causing recessive genes that could be inherited by their children. Carrier testing is designed for healthy people who have no symptoms of disease, but who are known to be at high risk because of family history.

Cell:

small, watery, membrane-bound compartment filled with chemicals; the basic subunit of any living thing.

Chemical base:

an essential building block. DNA contains four complementary bases: adenine, which pairs with thymine, and cytosine, which pairs with guanine. In RNA, thymine is replaced by uracil.

Chromosomes:

structures found in the nucleus of a cell, which contain the genes. Chromosomes come in pairs, and a normal human cell contains 46 chromosomes, 22 pairs of autosomes and two sex chromosomes.

Clone:

a group of identical genes, cells, or organisms derived from a single ancestor.

Cloning:

the process of making genetically identical copies.

Contig maps:

types of physical DNA maps that consist of overlapping segments of DNA (contigs) that, taken together, completely represent that section of the genome. (See Physical maps.)

Colonoscopy:

examination of the colon through a flexible, lighted instrument called a colonoscope.

Crossing over:

a phenomenon, also known as recombination, that sometimes occurs during the formation of sperm and egg cells (meiosis); a pair of chromosomes (one from the mother and the other from the father) break and trade segments with one another.

Cystic fibrosis:

an inherited disease in which a thick mucus clogs the lungs and blocks the ducts of the pancreas.

Cytoplasm:

the cellular substance outside the nucleus in which the cell's organelles are suspended.

Dementia:

severe impairment of mental functioning.

DNA:

the substance of heredity; a large molecule that carries the genetic information that cells need to replicate and to produce proteins.

DNA repair genes:

certain genes that are part of a DNA repair pathway; when altered, they permit mutations to pile up throughout the DNA.

DNA sequencing:

determining the exact order of the base pairs in a segment of DNA.

Dominant allele:

a gene that is expressed, regardless of whether its counterpart allele on the other chromosome is dominant or recessive. Autosomal dominant disorders are produced by a single mutated dominant allele, even though its corresponding allele is normal. (See Recessive allele.)

Enzyme:

a protein that facilitates a specific chemical reaction.