Selfish DNA
Encyclopedia
Selfish DNA refers to those sequences of DNA
which, in their purest form, have two distinct properties: (1) the DNA sequence spreads by forming additional copies of itself within the genome
; and (2) it makes no specific contribution to the reproductive success
of its host organism
.
This idea was sketched briefly by Richard Dawkins in his 1976 book The Selfish Gene
and was explicitly exposed in two 1980 articles in Nature
magazine. According to one of these articles:
The selfish DNA can be considered an efficient replicator that follows another way of increasing in number.
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
which, in their purest form, have two distinct properties: (1) the DNA sequence spreads by forming additional copies of itself within the genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
; and (2) it makes no specific contribution to the reproductive success
Reproductive success
Reproductive success is defined as the passing of genes onto the next generation in a way that they too can pass those genes on. In practice, this is often a tally of the number of offspring produced by an individual. A more correct definition, which incorporates inclusive fitness, is the...
of its host organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
.
This idea was sketched briefly by Richard Dawkins in his 1976 book The Selfish Gene
The Selfish Gene
The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...
and was explicitly exposed in two 1980 articles in Nature
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...
magazine. According to one of these articles:
The selfish DNA can be considered an efficient replicator that follows another way of increasing in number.
Examples
- TransposonTransposonTransposable elements are sequences of DNA that can move or transpose themselves to new positions within the genome of a single cell. The mechanism of transposition can be either "copy and paste" or "cut and paste". Transposition can create phenotypically significant mutations and alter the cell's...
s copy themselves to different lociLocus (genetics)In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
inside the genome. These elements constitute a large fraction of eukaryotic genome sizeGenome sizeGenome size is the total amount of DNA contained within one copy of a single genome. It is typically measured in terms of mass in picograms or less frequently in Daltons or as the total number of nucleotide base pairs typically in megabases . One picogram equals 978 megabases...
s (C-valueC-valueThe term C-value refers to the amount of DNA contained within a haploid nucleus or one half the amount in a diploid somatic cell of a eukaryotic organism, expressed in picograms...
s): about 45% of the human genomeHuman genomeThe human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs plus the small mitochondrial DNA. 22 of the 23 chromosomes are autosomal chromosome pairs, while the remaining pair is sex-determining...
is composed of transposons and their defunct remnants.
- Homing endonuclease genes cleave DNA at its own site on the homologous chromosomeHomologous chromosomeHomologous chromosomes are chromosome pairs of approximately the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding loci. One homologous chromosome is inherited from the organism's mother; the other from the organism's father...
, triggering the DNA double-stranded break repair system, which "repairs" the break by copying the HEG onto the homologous chromosome. HEGs have been characterized in yeastYeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
, and can only survive by passing between multiple isolated populations or species.
- Supernumerary B chromosomeB chromosomeIn addition to the normal karyotype, wild populations of many animal, plant, and fungi species contain B chromosomes . By definition, these chromosomes are not essential for the life of a species, and are lacking in some of the individuals...
s are nonessential chromosomes that are transmitted in higher-than-expected frequencies, which leads to their accumulation in progenies.