Thursday, October 1, 2009

Inversions (Short Note)

It is a type of chromosomal aberration in which a segment of chromosome is turned around 180º and is reinserted into the chromosome. An inversion does not involve a loss of genetic information but simply rearranges the linear gene sequence. An inversion involves two breaks along the length of the chromosome prior to the reinsertion of the inverted segments. The inverted segment may be short or quite long and may or may not include the Centromere. If the Centromere is not the part of the rearranged chromosome segment, the inversion is said to be Para centric, if the Cetromere is a part of the inverted segment, the inversion is known as Peri centric.

The organisms in which one inverted chromosome and one non inverted homologue is present are called Inversion heterozygotes. Normal linear pairing between such chromosomes is not possible until they form inversion loop. In other cases no loop can be formed and the homologues are seem to synapse every where but along the length of the inversion, where they appear separated if crossing over does not occur within the inverted segment of the inversion heterozygote, the homologues will segregrate normally.

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