Concerted evolution

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Concerted evolution is the phenomenon where paralogous genes within one species are more closely related to one another than to members of the same gene family in closely related species. In other terms, when specific members of a family are investigated, a greater amount of similarity is found within a species rather than between species. [1] This is suggesting that members within this family do not in fact evolve independently of one another. [2]

Contents

The concept of concerted evolution is a molecular process which leads to the homogenization of DNA sequences. [1]

As shown from the diagram on the right, as each organism evolves, it creates a species that is more closely related to their genes than anyone else in their species. This is demonstrated by the different colors of circles. If each different color is representing a different organism in one species, this is showing that once the blue and the orange reproduce, they create organisms that are incredibly alike to them (thus they are represented as the same color)

This fundamental process operates in all organisms, even if it does not seem ultimately present at every moment.

Causes

Concerted evolution (phenomenon of duplicated genes) may often be caused by the genetic exchange known as gene conversion. [3] This other phenomenon is known as the "non-reciprocal exchange of genetic material between homologous sequences." [3]

Gene conservation can do a few things...

...thus playing a role in concerted evolution.

Gene conversion is also reliant on the gene sequences that are involved in the current process. Some entire gene sequences have undergone the process of concerted evolution whereas others have a more mosaic pattern where some genes are homogenized, and others diverge without this conversion. [3]

Example

An example can be seen in bacteria: Escherichia coli (can cause severe food poisoning in hosts) has seven operons encoding various ribosomal RNA genes. For each of these genes, rDNA sequences are essentially identical among all of the seven operons (sequence divergence of only 0.195%). In a closely related species, Haemophilus influenzae its six ribosomal RNA operons are entirely identical. When the 2 species are compared together however, the sequence divergence of the 16S rRNA gene between them is 5.90%. [1]

Factors affecting the rate of concerted evolution

  1. The specific number of repeats counted [4]
  2. The arrangement of those repeats aforementioned (dispersed vs. clustered) [4]
  3. Relative sizes of slowly and rapidly evolving regions (within that repeating unit) [4]
    1. Noncoding regions evolve very rapidly
    2. Coding regions evolve very slowly
  4. Restriction on homogeneity [4]
  5. Population size [4]
  6. Requirement of doses [4]

Requirements

Hypotheses to explain concerted evolution

  1. High sequence similarity between paralogs may be maintained by homologous recombination events that lead to gene conversion, effectively copying some sequence from one and overwriting the homologous region in the other. Another possible hypothesis that has yet to be disproved is that rapid waves of gene duplication are responsible for the apparently "concerted" homogeneity of tandem and unlinked repeats seen in concerted evolution.
  2. Rapid amplification of a gene, usually assisted by recombination events in IS elements, in bacteria, or in other repetitive genetic elements (ERV, LINE, SINE, etc.), for example, in eukaryotes. Unchecked transposition events of these transposable elements are thought to be associated with increases in the copy number of the gene.
  3. In sexually reproducing organisms unequal crossing over during meiosis may be responsible for amplification due to misalignment of repeated sequences.
  4. Redistribution of genes requires transposition, probably assisted by the same repetitive genetic elements as in 1).
  5. Homogenization of alleles by gene conversion may also play a role in sexually reproducing organisms. Some genes may be more prone to gene conversion than others[ citation needed ], thus reinforcing the unity of the genes within a gene family of a species.

Evolution and speciation

Findings of concerted evolution, particularly in ribosomal DNA genes, led the Cambridge molecular geneticist Gabriel Dover to his controversial proposal of molecular drive, which in his view was an evolutionary principle distinct both from natural selection and from genetic drift. Closely related species or even populations may differ in their nucleolus organizing regions (NORs), which are genomic regions that contain many copies of ribosomal RNA genes in eukaryotes, typically found within or adjacent to highly repetitive parts of the genome such as centromeres or telomeres in mammals such as the house mouse Mus musculus [5] or insects such as the grasshopper Podisma pedestris . [6]

Further research

The link between concerted evolution or molecular drive both playing a role in speciation is currently unknown. While this is not currently correlated, it seems entirely possible that for example some hybrids or backcrosses between species with different nucleolar organizing regions/ribosomal DNA repeat regions may have reduced fitness as a result of over- or under-expression of ribosomal RNA.

Related Research Articles

<span class="mw-page-title-main">Genome</span> All genetic material of an organism

A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA. The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as regulatory sequences, and often a substantial fraction of junk DNA with no evident function. Almost all eukaryotes have mitochondria and a small mitochondrial genome. Algae and plants also contain chloroplasts with a chloroplast genome.

<span class="mw-page-title-main">Transposable element</span> Semiparasitic DNA sequence

A transposable element (TE), also transposon, or jumping gene, is a type of mobile genetic element, a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size.

Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules. Other functional regions of the non-coding DNA fraction include regulatory sequences that control gene expression; scaffold attachment regions; origins of DNA replication; centromeres; and telomeres. Some non-coding regions appear to be mostly nonfunctional, such as introns, pseudogenes, intergenic DNA, and fragments of transposons and viruses. Regions that are completely nonfunctional are called junk DNA.

Molecular evolution describes how inherited DNA and/or RNA change over evolutionary time, and the consequences of this for proteins and other components of cells and organisms. Molecular evolution is the basis of phylogenetic approaches to describing the tree of life. Molecular evolution overlaps with population genetics, especially on shorter timescales. Topics in molecular evolution include the origins of new genes, the genetic nature of complex traits, the genetic basis of adaptation and speciation, the evolution of development, and patterns and processes underlying genomic changes during evolution.

Gene duplication is a major mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.

<span class="mw-page-title-main">Gene family</span> Set of several similar genes

A gene family is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions. One such family are the genes for human hemoglobin subunits; the ten genes are in two clusters on different chromosomes, called the α-globin and β-globin loci. These two gene clusters are thought to have arisen as a result of a precursor gene being duplicated approximately 500 million years ago.

The ribosomal DNA consists of a group of ribosomal RNA encoding genes and related regulatory elements, and is widespread in similar configuration in all domains of life. The ribosomal DNA encodes the non-coding ribosomal RNA, integral structural elements in the assembly of ribosomes, its importance making it the most abundant section of RNA found in cells of eukaryotes. Additionally, these segments includes regulatory sections, such as a promotor specific to the RNA polymerase I, as well as both transcribed and non-transcribed spacer segments.

Repeated sequences are short or long patterns that occur in multiple copies throughout the genome. In many organisms, a significant fraction of the genomic DNA is repetitive, with over two-thirds of the sequence consisting of repetitive elements in humans. Some of these repeated sequences are necessary for maintaining important genome structures such as telomeres or centromeres.

Genetics, a discipline of biology, is the science of heredity and variation in living organisms.

Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion. Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another.

Interspersed repetitive DNA is found in all eukaryotic genomes. They differ from tandem repeat DNA in that rather than the repeat sequences coming right after one another, they are dispersed throughout the genome and nonadjacent. The sequence that repeats can vary depending on the type of organism, and many other factors. Certain classes of interspersed repeat sequences propagate themselves by RNA mediated transposition; they have been called retrotransposons, and they constitute 25–40% of most mammalian genomes. Some types of interspersed repetitive DNA elements allow new genes to evolve by uncoupling similar DNA sequences from gene conversion during meiosis.

<span class="mw-page-title-main">Conserved sequence</span> Similar DNA, RNA or protein sequences within genomes or among species

In evolutionary biology, conserved sequences are identical or similar sequences in nucleic acids or proteins across species, or within a genome, or between donor and receptor taxa. Conservation indicates that a sequence has been maintained by natural selection.

Exon shuffling is a molecular mechanism for the formation of new genes. It is a process through which two or more exons from different genes can be brought together ectopically, or the same exon can be duplicated, to create a new exon-intron structure. There are different mechanisms through which exon shuffling occurs: transposon mediated exon shuffling, crossover during sexual recombination of parental genomes and illegitimate recombination.

<span class="mw-page-title-main">Gene cluster</span> Group of related genes in genomic DNA

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 often located within a few thousand base pairs of each other. The size of gene clusters can vary significantly, from a few genes to several hundred genes. Portions of the DNA sequence of each gene within a gene cluster are found to be identical; however, the protein encoded by each gene is distinct from the proteins encoded by the other genes within the cluster. Gene clusters often result from expansions of a single gene caused by repeated duplication events, and may be observed near one another on the same chromosome or on different, but homologous chromosomes. An example of a gene cluster is the Hox gene, which is made up of eight genes and is part of the Homeobox gene family.

Molecular drive is a term coined by Gabriel Dover in 1982 to describe evolutionary processes that change the genetic composition of a population through DNA turnover mechanisms. Molecular drive operates independently of natural selection and genetic drift.

Helitrons are one of the three groups of eukaryotic class 2 transposable elements (TEs) so far described. They are the eukaryotic rolling-circle transposable elements which are hypothesized to transpose by a rolling circle replication mechanism via a single-stranded DNA intermediate. They were first discovered in plants and in the nematode Caenorhabditis elegans, and now they have been identified in a diverse range of species, from protists to mammals. Helitrons make up a substantial fraction of many genomes where non-autonomous elements frequently outnumber the putative autonomous partner. Helitrons seem to have a major role in the evolution of host genomes. They frequently capture diverse host genes, some of which can evolve into novel host genes or become essential for Helitron transposition.

A conserved non-coding sequence (CNS) is a DNA sequence of noncoding DNA that is evolutionarily conserved. These sequences are of interest for their potential to regulate gene production.

<span class="mw-page-title-main">Unequal crossing over</span> Chromosomal crossover resulting in gene duplication or deletion

Unequal crossing over is a type of gene duplication or deletion event that deletes a sequence in one strand and replaces it with a duplication from its sister chromatid in mitosis or from its homologous chromosome during meiosis. It is a type of chromosomal crossover between homologous sequences that are not paired precisely. Normally genes are responsible for occurrence of crossing over. It exchanges sequences of different links between chromosomes. Along with gene conversion, it is believed to be the main driver for the generation of gene duplications and is a source of mutation in the genome.

<span class="mw-page-title-main">Jürgen Brosius</span> German molecular geneticist and evolutionary biologist

Jürgen Brosius is a German molecular geneticist and evolutionary biologist. He was professor and director of the Institute of Experimental Pathology at the University of Münster. Some of his scientific contributions involve the first genetic sequencing of a ribosomal RNA operon, the design of plasmids for studying gene expression, expression vectors for high-level production of recombinant proteins and RNA, RNA biology, RNomics as well as the significance of retroposition for plasticity and evolution of genomes, genes and gene modules including regulatory sequences or elements.

This glossary of cellular and molecular biology is a list of definitions of terms and concepts commonly used in the study of cell biology, molecular biology, and related disciplines, including molecular genetics, biochemistry, and microbiology. It is split across two articles:

References

  1. 1 2 3 Liao, D (1999). "Concerted evolution: molecular mechanism and biological implications". Am J Hum Genet. 64 (1): 24–30. doi:10.1086/302221. PMC   1377698 . PMID   9915939.
  2. ↑ Liao, Daiqing (1999-01-01). "Concerted Evolution: Molecular Mechanism and Biological Implications". The American Journal of Human Genetics. 64 (1): 24–30. doi:10.1086/302221. ISSN   0002-9297. PMC   1377698 . PMID   9915939.
  3. 1 2 3 Carson, Andrew R; Scherer, Stephen W (2009-07-07). "Identifying concerted evolution and gene conversion in mammalian gene pairs lasting over 100 million years". BMC Evolutionary Biology. 9: 156. doi: 10.1186/1471-2148-9-156 . ISSN   1471-2148. PMC   2720389 . PMID   19583854.
  4. 1 2 3 4 5 6 7 8 "Concerted Evolution - [PPT Powerpoint]". vdocuments.mx. Retrieved 2022-05-02.
  5. ↑ Britton-Davidian, J (2012). "Chromosomal dynamics of nucleolar organizer regions (NORs) in the house mouse: micro-evolutionary insights". Heredity. 108 (1): 68–74. doi: 10.1038/hdy.2011.105 . PMC   3238117 . PMID   22086078.
  6. ↑ Bella, JL (1991). "Sex chromosome and autosome divergence in Podisma (Orthoptera) in western Europe". Genetics Selection Evolution. 23 (1): 5–13. doi: 10.1186/1297-9686-23-1-5 . PMC   2711129 .
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