Tandemly arrayed genes (TAGs) are a
gene cluster
A gene family is a set of homologous genes within one organism. A gene cluster is a group of two or more genes found within an organism's DNA that encode similar polypeptides, or proteins, which collectively share a generalized function and are o ...
created by
tandem duplications, a process in which one gene is duplicated and the copy is found adjacent to the original. They serve to encode large numbers of
gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s at a time.
TAGs represent a large proportion of genes in a genome, including between 14% to 17% of the human, mouse, and rat genomes. TAG clusters may have as few as two genes, with small clusters predominating, but may consist of hundreds of genes. An example are tandem clusters of
rRNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from riboso ...
encoding genes. These genes are transcribed faster than they would be if only a single copy of the gene was available. Additionally, a single RNA gene may not be able to provide enough RNA, but tandem repeats of the gene allow sufficient RNA to be produced. For example, cells in a
human embryo
Human embryonic development, or human embryogenesis, is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of d ...
contain between five and ten million
ribosomes
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to ...
, and cell number doubles within 24 hours. In order to provide the necessary ribosomes, multiple
RNA polymerase
In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template.
Using the enzyme helicase, RNAP locally opens the ...
s must consecutively transcribe multiple rRNA genes.
In some species, such as
Arabidopsis thaliana
''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land.
A winter ...
and
Oryza sativa, most TAGs are the result of unequal
chromosomal crossover
Chromosomal crossover, or crossing over, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes. It is one of the final phases of geneti ...
during
genetic recombination
Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukary ...
.
See also
*
Satellite DNA Satellite DNA consists of very large arrays of tandemly repeating, non-coding DNA. Satellite DNA is the main component of functional centromeres, and form the main structural constituent of heterochromatin.
The name "satellite DNA" refers to the p ...
*
Tandem repeats
Notes
References
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Repetitive DNA sequences
Genes
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