Gene (redirected from allelic g's)

gene (jen) the biologic unit of heredity, self-reproducing and located at a definite position (locus) on a particular chromosome.

---

allelic gene  allele.

chimeric gene  an artificial gene constructed by juxtaposition of fragments of unrelated genes or other DNA segments, which may themselves have been altered.

complementary genes  two independent pairs of nonallelic genes, neither of which will produce its effect in the absence of the other.

dominant gene  one that is phenotypically expressed when present in homozygotes or heterozygotes.

H gene , 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 genes  genes in the nonhomologous region of the Y chromosome.

immune response (Ir) genes  genes of the major histocompatibility complex that govern the immune response to individual immunogens.

Is genes  genes that govern the formation of suppressor T lymphocytes.

lethal gene  one whose presence brings about the death of the organism or permits survival only under certain conditions.

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.

recessive gene  one that produces an effect in the organism only when it is homozygous.

regulator gene , regulatory gene

1. in genetic theory, one that synthesizes repressor, a substance that through interaction with the operator gene switches off the activity of the structural genes associated with it in the operon.

2. any gene whose product affects the activity of other genes.

repressor gene  regulator g. (1).

sex-linked gene  one carried on a sex chromosome, especially on an X chromosome.

split gene  a gene containing multiple exons and at least one intron.

structural gene  one that specifies the amino acid sequence of a polypeptide chain.

---

gene (jn)

n.

A hereditary unit that occupies a specific location on a chromosome, determines a particular characteristic in an organism by directing the formation of a specific protein, and is capable of replicating itself at each cell division.

---

Gene

A building block of inheritance, which contains the instructions for the production of a particular protein, and is made up of a molecular sequence found on a section of DNA. Each gene is found on a precise location on a chromosome.

Mentioned in: Acoustic Neuroma, Albinism, Birth Defects, Blood Typing and Crossmatching, Cutis Laxa, Familial Polyposis, Gene Therapy, Genetic Testing, Periodic Paralysis, Phenylketonuria, Polydactyly and Syndactyly, Porphyrias, Prader-Willi Syndrome, Pseudoxanthoma Elasticum, Retinoblastoma, Situs Inversus, Von Willebrand Disease, Wilson Disease, Wiskott-Aldrich Syndrome

---

gene,

n the unit of heredity that is made of a DNA sequence occupying a specific location on a chromosome and codes for a polypeptide chain.

gene pool,

n the sum of genes in a given population.

---

gene,

n See family practice.

(ho´meoboks”),
n a gene containing a DNA sequence called the homeobox, which is very similar between species and encodes a DNA-binding domain in the resulting protein molecule. Homeobox genes usually play a role in controlling development of the organism.

gene locus,

n See locus, gene.

gene, sex-linked,

n a gene located in a sex chromosome.

gene therapy,

n a procedure that involves injection of “health genes” into the bloodstream of a patient to cure or treat a hereditary disease or similar illness.

---

gene

the unit of heredity most simply defined as a specific segment of DNA, usually in the order of 1000 nucleotides, that specifies a single polypeptide. Many phenotypic characteristics are determined by a single gene, while others are multigenic. Genes are specifically located in linear order along the single DNA molecule that makes up each chromosome. All eukaryotic cells contain a diploid (2n) set of chromosomes so that two copies of each gene, one derived from each parent, are present in each cell; the two copies often specify a different phenotype, i.e. the polypeptide will have a somewhat different amino acid composition. These alternative forms of gene, both within and between individuals, are called alleles. Genes determine the physical (structural genes), the biochemical (enzymes), physiological and behavioral characteristics of an animal.

The formation of gametes (sperm, ova) involves a process of meiosis, which allows crossing over between four pairs of chromosomes, two derived from each parent, which means that new forms of a particular chromosome are created. Gamete formation also results in cells (gametes) with a haploid (n) set of chromosomes that in fertilization creates a new individual, which is a recombinant of 2n chromosomes, half derived by way of the ovum from the mother and half via the spermatozoa from the father.

Changes in the nucleotide sequence of a gene, either by substitution of a different nucleotide or by deletion or insertion of other nucleotides, constitute mutations which add to the diversity of animal species by creating different alleles and can be used as a basis for genetic selection of different phenotypes. Some mutations, be they a single base change in a single gene or a major deletion, are lethal.

---

gene action

the way in which genes exert their effects on tissues or processes, e.g. by being dominant or recessive, or partially so, being absent, being sex-linked, being involved in chromosomal aberrations.

allelic g's

different forms of a particular gene usually situated at the same position (locus) in a pair of chromosomes.

gene amplification

see gene duplication (below).

gene bank

the collection of DNA sequences in a given genome. Called also gene library.

barring gene

responsible for the barred pattern on the feathers of Barred Plymouth Rock birds.

gene box

see box (4).

gene clone

see clone.

gene cluster

a group of related genes derived from a common ancestral gene, located closely together on the same chromosome. Called also multigene family.

complementary g's

two independent pairs of nonallelic genes, neither of which is functional without the other.

gene conversion

a non-reciprocal exchange of DNA elements during meiosis which results in a functional rearrangement of chromosomal DNA.

dhfr gene

dihydrofolate reductase gene; an enzyme required to maintain cellular concentrations of H₂ folate for nucleotide biosynthesis, and which has been used as a 'selective marker'; cells lacking the enzyme only survive in media containing thymidine, glycine and purines; mutant cells (dhfr) transfected with DNA that is dhfr' can be selectively grown in medium lacking these elements.

diversity (D) gene

genes located in diversity (D) segment; contribute to the hypervariable region of immunoglobulins.

dominant gene

one that produces an effect (the phenotype) in the organism regardless of the state of the corresponding allele. Examples of traits determined by dominant genes are short hair in cats and black coat color in dogs.

gene duplication

as a result of non-homologous recombination, a chromosome carries two or more copies of a gene.

gene expression

see expression (3).

gene frequency

the proportion of the substances or animals in the group which carry a particular gene.

holandric g's

genes located on the Y chromosome and appearing only in male offspring.

immune response (Ir) g's

genes of the major histocompatibility complex (MHC) that govern the immune response to individual immunogens.

jumping gene

see mobile dna.

gene knockout

replacement of a normal gene with a mutant allele, as in gene knockout mice.

lethal gene

one whose presence brings about the death of the organism or permits survival only under certain conditions.

gene library

see gene bank (above).

gene locus

see locus.

mutant gene

one that has undergone a detectable mutation.

non-protein encoding gene

the final products of some genes are RNA molecules rather than proteins.

overlapping g's

when more than one mRNA is transcribed from the same DNA sequence; the mRNAs may be in the same reading frame but of different size or they may be in different reading frames.

gene pool

total of all genes possessed by all members of the population which are capable of reproducing during their lifetime.

gene probe

see probe (2).

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.

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.

reporter gene

one that produces products which can be measured and therefore used as an indicator of whether a DNA construct has successfully been transferred.

sex-linked gene

one that is carried on a sex chromosome, especially an X chromosome.

gene splicing

see splicing.

structural gene

nucleotide sequences coding for proteins.

gene therapy

the insertion of functional genes into cells of the host in order to alter its phenotype, usually used to treat an inherited defect.

gene transcription

see transcription.

gene transfer

see recombination.

tumor suppressor g's

a class of genes that encode proteins that normally suppress cell division that when mutated allow cells to continue unrestricted cell division and may result in a tumor.

---

gene Genetics Classic mendelian definition A unit of inheritance carrying a single trait and recognized by its ability to mutate and undergo recombination–this definition is widely recognized as primitive Current definition A segment of DNA nucleotides, comprised of 70 to 30,000 bp including introns, that encodes a sequence of mRNA, capable of giving rise to a functional producte–eg, enzyme, hormone, receptor–polypeptide; genes may be structural, and form cell components, or functional, and have a regulatory role; a biological unit of heredity which is self-reproducing and located at a definite position on a particular chromosome; genes are working subunits of DNA; each of the body's 50,000 to 100,000 genes contains the code for a specific product, commonly for making a specific protein–eg an enzyme; the functional and physical unit of heredity passed from parent to offspring. See Cellular oncogene, Crime gene, Expressed gene, Functional gene, Housekeeping gene, Lethal gene, Mutable gene, Mutator gene, Pseudogene, Reporter gene, Structural gene, Suppressor gene, Tumor suppressor. Cf Chromosome.