Final answer:
Chromosome inversions involve the detachment, 180° rotation, and reinsertion of a chromosome segment. Pericentric inversions include the centromere and can affect chromosomal arm lengths, while paracentric inversions do not involve the centromere. Such inversions can have evolutionary consequences, as seen in human chromosome 18 in comparison to chimpanzees.
Step-by-step explanation:
Chromosome Inversions
A chromosome inversion refers to the detachment, 180° rotation, and reinsertion of part of a chromosome. This process can occur due to mechanical shear or the action of transposable elements. While inversions usually just change the gene orientation without affecting their functions, they can sometimes lead to functional changes if regulators of gene expression are moved out of position relative to their targets, potentially causing abnormal levels of gene products.
Pericentric inversions involve the centromere and can alter the relative lengths of chromosomal arms. On the other hand, paracentric inversions occur outside of the centromere and do not involve changes in arm lengths. During meiosis, inversions can be identified as homologous chromosomes with rearrangements must contort to align properly.
Not all chromosomal rearrangements have detrimental effects. For instance, a pericentric inversion in chromosome 18 is believed to have played a role in human evolution, a change not found in chimpanzees, our closest genetic relatives. This indicates that in some cases, inversions can contribute to significant evolutionary developments.