Why is pericentric inversion of chromosomes more severe than paracentric inversion?

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enginr eNotes educator| Certified Educator

Chromosomal inversion simply means that a piece of the chromosome has become reversed in orientation. If the reversed segment does not span the centomere, it is called paracentric inversions. If the segment does span the centomere, it is a pericentric inversion.

The majority of the time, chromosomal inversions do not result in large errors. The individual still maintains all the genes they had before the inversion.

Pericentric inversions in and of themselves are not likely to be more problematic. It is when a pericentric inversion is combined with crossing over that can result in severe abnormalities because genes can be lost in this process. 

Please see the attached sketch. Inversions are highlighted in red. The first chromosome is the original. The second shows a paracentric inversion. The second shows a pericentric inversion. The final shows a pericentric inversion and crossing over - both the chromatids below the centromere have been swapped entirely. The blue and yellow highlighted areas show the segments which are now repeated twice on each sister chromatid. The left chromatid has two copies of the yellow segment and has lost the blue segment entirely. The reverse is true of the right chromatid. 

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