Winkler, Malcolm E. Department of Microbiology and Molecular Genetics, University of Texas, Houston, Texas.
Last reviewed:April 2019
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- Molecular biology
- Flow of genetic information
- Isolating genes
- Links to Primary Literature
- Additional Readings
The basic unit in inheritance consisting of DNA. A gene is composed of a deoxyribonucleic acid (DNA) sequence that contains the elements required for transcription of a complementary ribonucleic acid (RNA), which is sometimes the functional gene product, but more often is converted into messenger RNAs (mRNAs) that specify the amino acid sequence of a protein product (Fig. 1). The facts of Mendelian inheritance indicate the presence of discrete hereditary units (genes) that replicate at each cell division, producing remarkably exact copies of themselves, and that in some highly specific way determine the characteristics of the individuals that bear them. The evidence also shows that each of these units may at times mutate to give a new equally stable unit (called an allele), which has more or less similar, but not identical, effects on the characters of its bearers. The criteria for the recognition that certain genes are alleles have been that they (1) arise from one another by a single mutation, (2) have similar effects on the characters of the organism, and (3) occupy the same locus (region) in the chromosome. It has long been known that there were a few cases in which these criteria did not give consistent results, but these were explained by special hypotheses in the individual cases. However, such cases have been found to be so numerous that they appear to be the rule rather than the exception. See also: Allele; Cell division; Chromosome; Deoxyribonucleic acid (DNA); Mendelism; Mutation; Protein; Recombination (genetics); Ribonucleic acid (RNA); Transcription
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