Webster's New World Medical Dictionary

gene deletion
The total loss or absence of a
gene. Gene deletion plays a role in birth defects and
in the development of cancer.
gene duplication
An extra copy of a gene. Gene
duplication is a key mechanism in evolution. After a
gene is duplicated, the once-identical genes can
undergo changes and diverge to create two different
genes.
gene expression
The translation of information
encoded in a gene into protein or RNA structures
that are present and operating in the cell. Expressed
genes include genes that are transcribed into mes-
senger RNA (mRNA) and then translated into pro-
tein, as well as genes that are transcribed into RNA,
such as transfer and ribosomal RNAs, but not trans-
lated into protein.
gene family
A group of genes that are related in
structure and often in function. The genes in a gene
family are descended from an ancestral gene. For
example, the hemoglobin genes belong to one gene
family that was created by gene duplication and
divergence.
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gene mapping
The charting of the positions of
genes on a DNA molecule or chromosome and the
distance, in linkage units or physical units, between
genes.
gene marker
A detectable genetic trait or distinc-
tive segment of DNA that serves as a landmark for a
target gene. Markers are on the same chromosome
as the target gene. They must be near enough to the
target gene to be genetically linked to it and to be
inherited, usually together with that gene, and
thereby serve as signposts to it.
gene product
The RNA or protein that results
from the expression of a gene. The amount of gene
product is a measure of the degree of gene activity.
gene testing
The testing of a sample of blood (or
another fluid or tissue) for evidence of a gene. The
aim of gene testing is usually to learn whether a
gene for a disease is present or absent.
gene therapy
The treatment of disease by replac-
ing, altering, or supplementing a gene that is absent
or abnormal and that is responsible for the disease.
general paresis
Progressive dementia and gen-
eralized paralysis due to chronic inflammation of the
covering and substance of the brain (meningoen-
cephalitis). General paresis is a part of late (tertiary)
syphilis and is very rare today. It occurs a decade or
more after the initial infection.