one of the biologic units of heredity, self-reproducing, and located at a definite position (locus) on a particular chromosome. Genes make up segments of the complex deoxyribonucleic acid
(DNA) molecule that controls cellular reproduction and function. There are thousands of genes in the chromosomes of each cell nucleus; they play an important role in heredity because they control the individual physical, biochemical, and physiologic traits inherited by offspring from their parents. Through the genetic code of DNA they also control the day-to-day functions and reproduction of all cells in the body. For example, the genes control the synthesis of structural proteins and also the enzymes that regulate various chemical reactions that take place in a cell.
The gene is capable of replication. When a cell multiplies by mitosis each daughter cell carries a set of genes that is an exact replica of that of the parent cell. This characteristic of replication explains how genes can carry hereditary traits through successive generations without change.
complementary g's two independent pairs of nonallelic genes, neither of which will produce its effect in the absence of the other.
DCC gene (deleted in colorectal carcinoma) a gene normally expressed in the mucosa of the colon but reduced or absent in a small proportion of patients with colorectal cancer.
one that produces an effect (the phenotype) in the organism regardless of the state of the corresponding allele. An example of a trait determined by a dominant gene is brown eye color. See also heredity
histocompatibility gene one that determines the specificity of tissue antigenicity (hla antigens) and thus the compatibility of donor and recipient in tissue transplantation and blood transfusion.
holandric g's genes located on the Y chromosome and appearing only in male offspring.
immune suppressor (Is) g's
genes that govern the formation of suppressor T lymphocytes
immunoglobulin g's the genes coding for immunoglobulin heavy and light chains, which are organized in three loci coding for κ light chains, λ light chains, and heavy chains.
lethal gene one whose presence brings about the death of the organism or permits survival only under certain conditions.
major gene a gene whose effect on the phenotype is always evident, regardless of how this effect is modified by other genes.
one that has undergone a detectable mutation
operator gene one serving as a starting point for reading the genetic code, and which, through interaction with a repressor, controls the activity of structural genes associated with it in the operon.
gene pool all of the genes possessed by all of the members of a population that will reproduce.
one that produces an effect in the organism only when it is transmitted by both parents, i.e., only when the individual is homozygous. See also heredity
regulator gene (repressor gene) one that synthesizes repressor, a substance which, through interaction with the operator gene, switches off the activity of the structural genes associated with it in the operon.
a gene carried on a sex chromosome (X or Y); only X linkage has clinical significance. See X-linked gene
structural gene one that forms templates for messenger RNA and is thereby responsible for the amino acid sequence of specific polypeptides.
tumor suppressor gene
a gene whose function is to limit cell proliferation and loss of whose function leads to cell transformation and tumor growth; called also antioncogene
X-linked gene a gene carried on the X chromosome; the corresponding trait, whether dominant or recessive, is always expressed in males, who have only one X chromosome. the term “X-linked” is sometimes used synonymously with “sex-linked,” since no genetic disorders have as yet been associated with genes on the Y chromosome.
tumor suppressor gene
a gene that encodes a protein involved in controlling cellular growth; inactivation of this type of gene leads to deregulated cellular proliferation, as in cancer.
See also: oncogene
In a person born with two normal copies of a tumor suppressor gene, both copies must be inactivated by spontaneous point mutation, deletion, or failure of expression before tumor formation occurs. An inherited mutation in a tumor suppressor gene is the basis of most familial predispositions to cancer. In a person so predisposed, malignant cellular proliferation does not occur until the remaining intact copy of the gene is inactivated by deletion of part or all of its chromosome. Of many tumor suppressor genes thus far identified, the p53 gene on chromosome 17, which encodes a phosphoprotein that suppresses cell proliferation, appears to be the most important. Mutations of p53 have been found in the DNA of more than half of all human cancers studied. Li-Fraumeni syndrome, characterized by early-onset carcinomas and sarcomas, is an inherited (autosomal dominant) mutation in the p53 tumor suppressor gene. BRCA1 and BRCA2, involved in familial early-onset breast cancer as well as ovarian and other cancers in people of both sexes, are tumor suppressor genes.