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An inversion is a chromosome rearrangement in which a segment of a chromosome becomes inverted within its original position. An inversion occurs when a chromosome undergoes a two breaks within the chromosomal arm, and the segment between the two breaks inserts itself in the opposite direction in the same chromosome arm.
A hypercentric or pericentric lens is a lens system where the entrance pupil is located in front of the lens, in the space where an object could be located. In a certain region, objects that are further away from the lens produce larger images than objects that are closer to the lens.
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]
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.
This is called circle inversion or plane inversion. The inversion taking any point P (other than O ) to its image P ' also takes P ' back to P , so the result of applying the same inversion twice is the identity transformation which makes it a self-inversion (i.e. an involution).
While the idea of dorsoventral axis inversion appears to be supported by morphological and molecular data, others have proposed alternative plausible hypotheses (reviewed in Gerhart 2000). [1] One assumption of the inversion hypothesis is that the common ancestor of protostomes and chordates already possessed an organized central nervous system ...
In this case the recombination sites are slightly asymmetric, which allows the enzyme to tell apart the left and right ends of the site. When generating products, left ends are always joined to the right ends of their partner sites, and vice versa. This causes different recombination hybrid sites to be reconstituted in the recombination products.
The term reflection is loose, and considered by some an abuse of language, with inversion preferred; however, point reflection is widely used. Such maps are involutions, meaning that they have order 2 – they are their own inverse: applying them twice yields the identity map – which is also true of other maps called reflections.