A chromosomal rearrangement in which a segment of genetic material is broken away from the chromosome, inverted from end to end, and re-inserted into the chromosome at the same breakage site. Balanced inversions (no net loss or gain of genetic material) are usually not associated with phenotypic abnormalities, although in some cases gene disruptions at the breakpoints can cause adverse phenotypic effects, including some known genetic diseases; unbalanced inversions (loss or gain of chromosome material) nearly always yield an abnormal phenotype.