immunoglobulin G

gene

[jēn] 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.allelic gene allele.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.dominant gene 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" >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 response (Ir) g's genes of the complex" >major histocompatibility complex that govern the immune response to individual immunogens.immune suppressor (Is) g's genes that govern the formation of suppressor lymphocytes" >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.K-ras gene a type of oncogene.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.mutant gene 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.recessive gene 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.sex-linked gene a gene carried on a sex chromosome (X or Y); only X linkage has clinical significance. See gene" >X-linked gene.gene splicing recombinant dna technology.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.

immunoglobulin G

n. Abbr. IgG The most abundant class of antibodies found in blood serum and lymph and active against bacteria, fungi, viruses, and foreign particles. Immunoglobulin G antibodies trigger action of the complement system.