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In genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar wor ...
, a chromosomal rearrangement is a mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...
that is a type of chromosome abnormality
A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where ther ...
involving a change in the structure of the native chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
. Such changes may involve several different classes of events, like deletions, duplications, inversions, and translocations
In genetics, chromosome translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes balanced and unbalanced translocation, with two main types: reciprocal-, and Robertsonian translocation. Reciprocal translo ...
. Usually, these events are caused by a breakage in the DNA double helices at two different locations, followed by a rejoining of the broken ends to produce a new chromosomal arrangement 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 ba ...
s, different from the gene order of the chromosomes before they were broken. Structural chromosomal abnormalities are estimated to occur in around 0.5% of newborn infants.
Some chromosomal regions are more prone to rearrangement than others and thus are the source of genetic diseases and cancer. This instability is usually due to the propensity of these regions to misalign during DNA repair
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA dam ...
, exacerbated by defects of the appearance of replication proteins (like FEN1
Flap endonuclease 1 is an enzyme that in humans is encoded by the ''FEN1'' gene.
Function
The protein encoded by this gene removes 5' overhanging "flaps" (or short sections of single stranded DNA that "hang off" because their nucleotide bases a ...
or Pol δ) that ubiquitously affect the integrity of the genome.
Complex chromosomal rearrangements (CCR) are rarely seen in the general population and are defined as structural chromosomal rearrangements with at least three breakpoints with exchange of genetic material between two or more chromosomes. Some forms of campomelic dysplasia
Campomelic dysplasia (CMD) is a genetic disorder characterized by bowing of the long bones and many other skeletal and extraskeletal features.
It can be lethal in the neonatal period due to respiratory insufficiency, but the severity of the disease ...
, for example, result from CCRs.
Heng and Gorelick and Heng reviewed evidence that sexual reproduction helps preserve species identity by acting as a coarse filter, weeding out chromosomal rearrangements, but permitting minor variation, such as changes at the nucleotide or gene level (that are often neutral) to pass through the sexual sieve.
It is possible that speciation
Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
frequently occurs when a population becomes fixed
Fixed may refer to:
* ''Fixed'' (EP), EP by Nine Inch Nails
* ''Fixed'', an upcoming 2D adult animated film directed by Genndy Tartakovsky
* Fixed (typeface), a collection of monospace bitmap fonts that is distributed with the X Window System
* ...
for one or more chromosomal rearrangements that reduce fitness when they are heterozygous
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
. This theory is lacking in theoretical support because mutations that cause a large reduction in fitness can only be fixed through genetic drift
Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Genetic drift may cause gene variants to disappear completely and there ...
in small, inbred
Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and o ...
populations, and the effects of chromosomal rearrangements on fitness are unpredictable and vary greatly in plant and animal species. However, a potential mechanism that could promote speciation is that rearrangements reduce gene flow more by suppressing recombination (and extending the effects of linked isolation genes) than by reducing fitness.
Exemplifying (extensive) chromosome rearrangements can be found in the complete and haplotype-resolved African cassava (TME204) genome that was reconstructed and made available using the Hi-C technology.
References
{{DEFAULTSORT:Rearrangements Cytogenetics Chromosomal abnormalities Modification of genetic information