paracentricity

Paracentricity is a term used in genetics to describe the state or quality of a chromosomal rearrangement that is paracentric. A paracentric rearrangement, specifically a paracentric inversion, occurs when a segment of a chromosome is flipped in orientation on one arm without involving the centromere. This contrasts with pericentric rearrangements, which include the centromere and typically affect both chromosome arms.

In meiosis, individuals heterozygous for a paracentric inversion experience distinctive meiotic outcomes if crossing over occurs within the inverted region. Such recombination can generate acentric fragments and dicentric chromatids, which are often nonfunctional and lead to nonviable gametes. As a result, recombination within the inverted interval is suppressed in many cases, preserving the gene order inside the inversion but reducing genetic exchange with the homologous chromosome.

Detection and study of paracentricity rely on cytogenetic methods, genomic sequencing, and population-genetic analyses. Researchers infer paracentric inversions through observed patterns of suppressed recombination, deviations in gene order, or direct identification of breakpoints that lie entirely on one chromosome arm. Paracentricity is typically discussed in contrast to pericentricity, where the inversion breakpoint spans the centromere and changes relative arm lengths.

Evolutionary and functional significance arises because paracentric inversions can maintain combinations of alleles across multiple loci, potentially contributing to local adaptation or reproductive isolation. However, the specific consequences depend on the inverted region’s gene content and the fitness effects of the involved alleles. The term paracentricity is most commonly used in chromosomal and evolutionary genetics literature.