Inversion in biology is the breaking of a chromosome in two places and the subsequent reordering re-insertion of the chromosome DNA. Inversions are divided into pericentric and paracentric types based on whether the centromere was involved.
Inversions usually induce small chromosomal inversions. A notable exception is the 3RP inversion of Drosophila melanogaster, which is several megabases in size. Pericentric inversions begin when a single crossover event occurs between the breakpoints of a heterozygote. This crossover produces unbalanced gametes carrying mutations such as deletions, insertions and zero or two centromeres. This may reduce fertility, making inversions underdominant processes that lower zygote fitness.
Pericentric inversions may avoid incurring damage to genetic fitness by suppressing recombination. These repressive inversions represent a small fraction of these processes. The damage of percentric inversions to genetic fitness varies between taxa and species. Plants are rendered more infertile by inversions than animals. Paracentric inversions are far less likely to cause mutation damage because they do not involve the centromere, the genetic locus that directs the behavior of the entire chromosome.
Even pericentric inversions often show no difference in genetic content before and after inversion, leading only to changes in the order of the DNA bases but not in the genetic information that is expressed.