An inversion is a type of chromosomal rearrangement where a piece of a chromosome breaks off and is reinserted ‘back to front’. There are two types of inversion: paracentric and pericentric. Inversions do not normally cause problems as the rearrangement does not involve loss or gain of genetic information. It may be problematic, however, if the organism is heterozygous for an inversion. In this case, there is increased production of abnormal chromatids due to unbalanced recombination across the span of the inversion.

Paracentric inversions do not involve the centromere of the chromosome, such that the break-point appears in only one arm of the chromosome. Pericentric inversions, by contrast, do involve the centromere and thus break-points appear in both arms of the chromosome.