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 chromosome (krō`məsōm')
..... Click the link for more information. . 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 (see nucleic acid nucleic acid, any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
..... Click the link for more information. ). 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 mutation, in biology, a sudden, random change in a gene , or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its
..... Click the link for more information. . 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.
..... Click the link for more information. .

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

See also gene therapy gene therapy, the use of genes and the techniques of genetic engineering in the treatment of a genetic disorder or chronic disease. There are many techniques of gene therapy, all of them still in experimental stages.
..... Click the link for more information. ; genetic engineering genetic engineering, the use of various methods to manipulate the DNA (genetic material) of cells to change hereditary traits or produce biological products.
..... Click the link for more information. .

gene

Unit of heredity that occupies a fixed position on a chromosome. Genes achieve their effects by directing protein synthesis. They are composed of DNA, except in some viruses that contain RNA instead. The sequence of nitrogenous bases along a strand of DNA determines the genetic code. When the product of a particular gene is needed, the portion of the DNA molecule that contains that gene splits, and a complementary strand of RNA, called messenger RNA (mRNA), forms and then passes to ribosomes, where proteins are synthesized. A second type of RNA, transfer RNA (tRNA), matches up the mRNA with specific amino acids, which combine in series to form polypeptide chains, the building blocks of proteins. Experiments have shown that many of the genes within a cell are inactive much or even all of the time, but they can be switched on and off. Mutations occur when the number or order of bases in a gene is disrupted. See also genetic engineering, genetics, Hardy-Weinberg law, Human Genome Project, linkage group.

gene (redirected from Gene bank)

gene

gene
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