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glossary:gene

Gene

Gene Definition

Gene the structural unit of inheritance in living organisms. A gene is, in essence, a segment of DNA that has a particular purpose, i.e., that codes for (contains the chemical information necessary for the creation of) a specific enzyme or other protein. The strands of DNA on which the genes occur are organized into chromosomes The nucleus of each eukaryotic (nucleated) cell has a complete set of chromosomes and therefore a complete set of genes. Each gene provides a blueprint for the synthesis (via RNA) of enzymes and other proteins and specifies when these substances are to be made. Genes govern both the structure and metabolic functions of the cells, and thus of the entire organism and, when located in reproductive cells, they pass their information to the next generation.

Chemically, each gene consists of a specific sequence of DNA building blocks called nucleotides. Each nucleotide is composed of three subunits: a nitrogen-containing compound, a sugar, and phosphoric acid. Genes may vary in their precise makeup from person to person, including, for example, one nucleotide in a certain location in some people but another nucleotide in that location in others. Geometrically, the gene is a double helix formed by the nucleotides. Gene loci are often interspersed with segments of DNA that do not code for proteins; these segments are termed “junk DNA.” When junk DNA occurs within a gene, the coding portions are called exons and the noncoding (junk) portions are called introns. Junk DNA makes up 97% of the DNA in the human genome, and, despite its name, is necessary for the proper functioning of the genes.

Each chromosome of each species has a definite number and arrangement of genes. Alteration of the number or arrangement of the genes can result in mutation When the mutation occurs in the germ cells (egg or sperm), the change can be transmitted to the next generation. Mutations that affect somatic cells can result in certain cancers cancer, in medicine, common term for neoplasms, or tumors, that are malignant. Like benign tumors, malignant tumors do not respond to body mechanisms that limit cell growth.

The scientific study of inheritance is genetics genome, or characteristic set of genes, that contains the total genetic information for an individual organism. In many familiar organisms two genes for each trait are present in each individual, and these paired genes, both governing the same trait, are called alleles.

The genetic makeup of an organism with reference to its set of genetic traits is called its genotype. The interaction of the environment and the genotype produces the observable attributes of the organism, or its phenotype. The sum total of the genes contained in an organism's full set of chromosomes is termed the genome. Scientists are working toward identifying the location and function of each gene in the human genome (see Human Genome Project Human Genome Project, which is an international scientific effort to map all of the genes on the 23 pairs of human chromosomes and, to sequence the 3.1 billion DNA base pairs that make up the chromosomes (see nucleic acid ).

The decoding of the first free-living organism (a bacterium, Hemophilus influenzae) was completed in 1995 by J. Craig Venter and Hamilton Smith.

Allele, allelomorph

(genetics) either of a pair (or series) of alternative forms of a gene that can occupy the same locus on a Threadlike strand of DNA in the cell nucleus that carries the genes in a linear order; “humans have 22 chromosome pairs plus two sex chromosomes”

Dominant gene

Gene that produces the same phenotype in the organism whether or not its allele identical; “the dominant gene for brown eyes”

Gene amplification

n. A cellular process characterized by the production of multiple copies of a particular gene or genes to amplify the phenotype that the gene confers on the cell. Drug resistance in cancer cells is linked to amplification of the gene that prevents absorption of the chemotherapeutic agent by the cell.

Gene chip

Aa microchip that holds DNA probes that form half of the DNA double helix and can recognize DNA from samples being tested

Gene delivery vector

A vector for delivering genes into cells

Gene expression

Conversion of the information encoded in a gene first into messenger RNA and then to a protein

Gene flow

n. Transfer of genes from one population to another of the same species, as by migration or the dispersal of seeds and pollen.

Gene frequency

n. The frequency of occurrence of an allele in relation to that of other alleles of the same gene in a population.

Gene locus

The specific place on a chromosome where a gene is located.

Locus: The place, in Latin.. In genetics, a locus is the place a gene occupies on a chromosome. One locus, two loci.

Gene regulation

Refers to the cellular control of the amount and timing of changes to the appearance of the functional product of a gene. Although a functional gene product may be an RNA or a protein, the majority of the known mechanisms regulate the expression of protein coding genes. Any step of the gene's expression may be modulated, from DNA-RNA transcription to the post-translational modification of a protein. Gene regulation gives the cell control over its structure and function, and is the basis for cellular differentiation, morphogenesis and the versatility and adaptability of any organism. Also known as (Regulation of gene expression )

Genetic marker

A specific gene that produces a recognizable trait and can be used in family or population studies holandric gene, Y-linked gene - a gene located on a Y chromosome

Genetic science, genetics

The branch of biology that studies heredity and variation in organisms

Homeotic gene

One the genes that are involved in embryologic development

Lethal gene

Any gene that has an effect that causes the death of the organism at any stage of life

Linkage group - linked genes

Any pair of genes that tend to be transmitted together; “the genes of Drosophila fall into four linkage groups”

Modifier gene, modifier

A gene that modifies the effect produced by another gene

Molecular biology

The branch of biology that studies the structure and activity of macromolecules essential to life (and especially with their genetic role)

Mutant gene

A gene that has changed so that the normal transmission and expression of a trait is affected

Nonallele

Genes that are not competitors at the same locus

Operator gene

A gene that activates the production of messenger RNA by adjacent structural genes

Oncogene

A gene that disposes normal cells to change into cancerous tumor cells

Polygene

A gene that by itself has little effect on the phenotype but which can act together with others to produce observable variations

Proto-oncogene

A normal gene that has the potential to become an oncogene

Recessive gene

Gene that produces its characteristic phenotype only when its allele is identical; “the recessive gene for blue eyes”

Regulator gene, regulatory gene

A gene that produces a repressor substance that inhibits an operator gene

Repressor gene

Gene that prevents a nonallele from being transcribed

Sequence

Serial arrangement in which things follow in logical order or a recurrent pattern; “the sequence of names was alphabetical”; “he invented a technique to determine the sequence of base pairs in DNA”

Structural gene

A gene that controls the production of a specific protein or peptide

Suppresser gene, suppressor gene, suppresser, suppressor

A gene that suppresses the phenotypic expression of another gene (especially of a mutant gene)

Transforming gene

A gene that disposes normal cells to change into cancerous tumor cells

Transgene

An exogenous gene introduced into the genome of another organism

X-linked gene

Agene located on an X chromosome

See also:

glossary/gene.txt · Last modified: 2012/10/16 14:40 (external edit)