What best describes a paracentric inversion?

A paracentric inversion is a specific type of chromosomal rearrangement where a segment of a chromosome is inverted, and this inversion occurs while excluding the centromere. This means that the inverted segment is located entirely within one arm of the chromosome, either the short arm (p) or the long arm (q), but not both. By maintaining this confinement within a single arm and not incorporating the centromere, the structure and function of the chromosome are altered without impacting the centromere's positioning.

The other options do not accurately describe a paracentric inversion. Sequences involving both arms would suggest a pericentric inversion, which includes the centromere. An implication of changing the overall number of chromosomes relates more closely to chromosomal duplications or deletions rather than to inversions, which do not change the chromosome count but can affect genetic expression and stability. The reference to including the centromere directly contradicts the definition of a paracentric inversion, as it specifically pertains to inversions that exclude it. Thus, the defining characteristic of a paracentric inversion is that it definitively involves sequences within one arm of the chromosome.