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Inversions can happen either through ectopic recombination between repetitive sequences, or through chromosomal breakage followed by non-homologous end joining. [4] Inversions are of two types: paracentric and pericentric. Paracentric inversions do not include the centromere, and both breakpoints
Inversions that exclude the centromere are known as paracentric inversions, which result in unbalanced gametes after meiosis. [2] During prophase of meiosis I, homologous chromosomes form an inversion loop and crossover occurs. If a paracentric inversion has occurred, one of the products will be acentric, while the other product will be dicentric.
The formation of dicentric chromosomes has been attributed to genetic processes, such as Robertsonian translocation [6] and paracentric inversion. [7] Dicentric chromosomes can have a variety of fates, including mitotic stability. [ 8 ]
Inversion was first noted in 1822 by the French zoologist Étienne Geoffroy Saint-Hilaire, when he dissected a crayfish (an arthropod) and compared it with the vertebrate body plan. The idea was heavily criticised, but periodically resurfaced, and is now supported by some molecular embryologists.
The classical example is the Drosophila w m4 (speak white-mottled-4) translocation.In this mutation, an inversion on the X chromosome placed the white gene next to pericentric heterochromatin, or a sequence of repeats that becomes heterochromatic. [3]
A chromosomal instability assay should measure not only whole chromosome change rates, but also the partial chromosomal changes such as deletions, insertions, inversion and amplifications to also take into account segmental aneuploidies. [5] This provides a more accurate determination of the presence of chromosome instability.
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Congenital hypertrichosis lanuginosa may be caused by a paracentric inversion mutation of the q22 band of chromosome 8; [1] however, it could also possibly be the result of a spontaneous genetic mutation rather than inheritance. [8] This form is an autosomal (not located on the sex chromosomes) dominant cutaneous disorder, that affects the skin ...