Chromosomal inversion
Encyclopedia
An inversion is a chromosome
rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric.
Paracentric inversions do not include the centromere
and both breaks occur in one arm of the chromosome. Pericentric inversions include the centromere and there is a break point in each arm.
Cytogenetic techniques may be able to detect inversions, or inversions may be inferred from genetic analysis
. Nevertheless, in most species small inversions go undetected. In insects with polytene chromosome
s, for example Drosophila
, preparations of larval salivary gland chromosomes allow inversions to be seen when they are heterozygous. This useful characteristic of polytene chromosome
s was first advertised by Theophilus Shickel Painter in 1933.
Inversions usually do not cause any abnormalities in carriers as long as the rearrangement is balanced with no extra or missing genetic information. However, in individuals which are heterozygous for an inversion, there is an increased production of abnormal chromatids (this occurs when crossing-over occurs within the span of the inversion). This leads to lowered fertility due to production of unbalanced gametes.
The most common inversion seen in humans is on chromosome 9, at inv(9)(p12q13). This inversion is generally considered to have no deleterious or harmful effects, but there is some evidence it leads to an increased risk for miscarriage for about 30% of affected couples.
An inversion does not involve a loss of genetic information, but simply rearranges the linear gene sequence.
Families that may be carriers of inversions may be offered genetic counseling
and genetic testing
.
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
rearrangement in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric.
Paracentric inversions do not include the centromere
Centromere
A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment...
and both breaks occur in one arm of the chromosome. Pericentric inversions include the centromere and there is a break point in each arm.
Cytogenetic techniques may be able to detect inversions, or inversions may be inferred from genetic analysis
Genetic analysis
Genetic analysis can be used generally to describe methods both used in and resulting from the sciences of genetics and molecular biology, or to applications resulting from this research....
. Nevertheless, in most species small inversions go undetected. In insects with polytene chromosome
Polytene chromosome
To increase cell volume, some specialized cells undergo repeated rounds of DNA replication without cell division , forming a giant polytene chromosome...
s, for example Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
, preparations of larval salivary gland chromosomes allow inversions to be seen when they are heterozygous. This useful characteristic of polytene chromosome
Polytene chromosome
To increase cell volume, some specialized cells undergo repeated rounds of DNA replication without cell division , forming a giant polytene chromosome...
s was first advertised by Theophilus Shickel Painter in 1933.
Inversions usually do not cause any abnormalities in carriers as long as the rearrangement is balanced with no extra or missing genetic information. However, in individuals which are heterozygous for an inversion, there is an increased production of abnormal chromatids (this occurs when crossing-over occurs within the span of the inversion). This leads to lowered fertility due to production of unbalanced gametes.
The most common inversion seen in humans is on chromosome 9, at inv(9)(p12q13). This inversion is generally considered to have no deleterious or harmful effects, but there is some evidence it leads to an increased risk for miscarriage for about 30% of affected couples.
An inversion does not involve a loss of genetic information, but simply rearranges the linear gene sequence.
Families that may be carriers of inversions may be offered genetic counseling
Genetic counseling
Genetic counseling or traveling is the process by which patients or relatives, at risk of an inherited disorder, are advised of the consequences and nature of the disorder, the probability of developing or transmitting it, and the options open to them in management and family planning...
and genetic testing
Genetic testing
Genetic testing is among the newest and most sophisticated of techniques used to test for genetic disorders which involves direct examination of the DNA molecule itself. Other genetic tests include biochemical tests for such gene products as enzymes and other proteins and for microscopic...
.