dominant gene

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

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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.

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dominant gene

n.

A gene that is expressed phenotypically in heterozygous or homozygous individuals.

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Dominant gene

A gene, whose presence as a single copy, controls the expression of a trait.

Mentioned in: Genetic Testing

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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.

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 major histocompatibility complex that govern the immune response to individual immunogens.

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.

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 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.

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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.

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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.