Final answer:
A chromosome inversion is a chromosomal structural change where a segment of DNA is rotated 180°. It changes the orientation of genes, potentially causing functional changes in gene expression. Inversions can be pericentric or paracentric.
Step-by-step explanation:
A chromosomal structural change in which a segment of DNA is rotated 180° is referred to as a chromosome inversion. It occurs when a section of a chromosome breaks off, flips, and rejoins the chromosome in the opposite orientation. Inversions only change the orientation of genes and are likely to have more mild effects than other chromosomal alterations. However, altered gene orientation can result in functional changes because regulators of gene expression could be moved out of position with respect to their targets. Chromosome inversions can be pericentric (including the centromere) or paracentric (occurring outside of the centromere).