Hypermedia Glossary Of Genetic Terms
|Transposition||Moving a DNA segment from one position of the genome to another or to a different genome. This change in genome structure happens in many organisms from bacteria to higher plants and animals.
Requirements: (1) intact inverted repeats at the ends of the IS-elements or transposons and (2) active transposase
The cut and paste mechanism leaves 'scars' in the donor molecule. Thus genes can be damaged or destroyed. Mutations may be induced via insertions into structure genes. Deletions or inversions may also be the result of a transposition.
History: Transposition was discovered by Barbara McClintock in the late 1940ies during her studies on maize genetics ('jumping genes'). 1983 she won the Nobel Prize for her transposon research.
|Deoxyribonucleic acid (DNA)||The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.|
|Genome||All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.|
|Inverted repeat (IR)||Nucleotide with opposite orientation of the base sequence and mostly below 50 base pairs. IRs are components of IS elements.|
|Insertion sequence (IS element)||Group of transposable elements that were detected by Saedler, Starling and Shapiro. They constist of 800 to 2000 base pairs and carry inverted repeats at their ends. The central part consists of reading frames and codes for transposases responsible for transposition.|
|Transposon (Tn)||DNA elements carrying genes for transposition and other genetic functions. The former genes enable those elements to move from one site on a chromosome to another. In many cases the latter genes enable bacteria to live in extreme environments. Transposons are much longer than IS elements. Some resemble, and may originate from, retroviruses.
Also called transposable element or 'jumping gene'.
|Transposase||Class of proteins responsible for transposition. One function is to prepare insertion by cutting at the integration site.|
|Gene||The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined. A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele.|
|Mutation||The term which De Vries introduced into biological literature for an abrupt change of genotype which is inherited. Any permanent and heritable change in DNA sequence. Types of mutations include point mutations, deletions, insertions, and changes in number and structure of chromosomes. (Cf. polymorphism)|
|Insertion||Addition of a DNA element into a chromosome.|
|Deletion||Loss of a segment of a chromosome as the genetical consequence of a transposition.|
|Inversion||The term introduccd by Sturtevant (1926) for the reversal of the linear sequence of the genes in a segment of a chromosome. In an inversion heterozygote one of the chromosomes contributed by one parent has an inverted segment while the homologous chromosome contributed by the other parent has the normal gene sequence.|
|Retrotransposon||Special transposon whose sequence is transcribed to RNA in the cell. After generation of the RNA strand a reverse transcriptase produced by the retrotransposon reconverts the RNA to DNA. This sequence is integrated into the original DNA strand at any position.|
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