paracentric

Paracentric is a term used in cytogenetics to describe a chromosomal inversion that does not involve the centromere. In a paracentric inversion, the inverted segment lies entirely on one arm of the chromosome, and the centromere is located outside the inverted region. This contrasts with pericentric inversions, in which the inverted segment includes the centromere and spans both chromosome arms.

Paracentric inversions arise from two breaks on the same chromosome arm followed by reinsertion in the opposite orientation. During meiosis in an individual heterozygous for a paracentric inversion, crossing over within the inverted loop can generate recombinant chromatids that are acentric (lacking a centromere) or dicentric (having two centromeres). Such products are typically unstable and lost during cell division, leading to unbalanced gametes. If no recombination occurs within the inverted segment, the carrier can be phenotypically normal but may have reduced fertility due to the production of inviable or unbalanced offspring after recombination.

Paracentric inversions are detected by karyotyping and other cytogenetic techniques, and their identification has clinical and research relevance for genetic counseling, fertility planning, and studying chromosomal polymorphisms in populations.