Paracentrici

Paracentrici, in genetics, refer to paracentric inversions, a type of chromosomal rearrangement in which a segment of a chromosome is inverted but does not include the centromere. They are contrasted with pericentric inversions, where the inverted segment does include the centromere. The term paracentrici is the plural form used in some languages; in English, the corresponding term is paracentric inversions.

Formation and meiotic behavior characterize paracentric inversions. They arise when two breaks occur on the same arm of a chromosome, and the intervening segment flips before rejoining. During meiosis in a heterozygote, homologous chromosomes pair through an inversion loop. If crossing over occurs within the inverted region, the recombinant chromatids typically become a dicentric chromosome and an acentric fragment, which are usually unstable and lost in cell division, producing gametes with duplications and deletions. If no crossing over occurs within the inverted region, balanced products can be transmitted and the carrier may appear normal.

Phenotypic effects depend on the genes involved and the breakpoints. Carriers often show no obvious phenotype, but paracentric inversions can reduce fertility due to unbalanced gametes and an increased risk of unbalanced offspring. Detection relies on cytogenetic techniques such as karyotyping and fluorescence in situ hybridization, with more modern approaches including array-based methods and sequencing to map breakpoints precisely. Paracentric inversions are observed across a wide range of species and can play a role in chromosomal evolution and, in some cases, reproductive isolation.