
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 Augustinians, Augustinian ...
, 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, ...
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 the ...
involving a change in the structure of the native
chromosome
A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...
. Such changes may involve several different classes of events, like
deletions,
duplications,
inversions, and
translocations. 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 has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
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 (biology), cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is cons ...
, exacerbated by defects of the appearance of replication proteins (like
FEN1 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, for example, result from CCRs.
Heng and Gorelick and Heng
[Gorelick R, Heng HH; Heng (2011). "Sex reduces genetic variation: a multidisciplinary review". Evolution. 65 (4): 1088–1098. doi:10.1111/j.1558-5646.2010.01173.x. PMID 21091466] 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.
[
In the ]liver
The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...
of mice, genome rearrangements do not increase with age until after 27 months when they increase rapidly.[Dollé ME, Giese H, Hopkins CL, Martus HJ, Hausdorff JM, Vijg J. Rapid accumulation of genome rearrangements in liver but not in brain of old mice. Nat Genet. 1997 Dec;17(4):431-4. doi: 10.1038/ng1297-431. PMID 9398844] In mouse brain
The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
the frequency of genome rearrangements is lower than in liver and this frequency does not increase with age.[
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'' (film), an upcoming animated film directed by Genndy Tartakovsky
* Fixed (typeface), a collection of monospace bitmap fonts that is distributed with the X Window System
* Fi ...
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.
Mos ...
. 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 random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance.
Genetic drift may cause gene va ...
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 an ...
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