transvection

Transvection is a genetic phenomenon in which regulatory elements on an allele can influence the expression of a gene on the paired homologous chromosome when the homologs are in close physical association. It was first described in Drosophila, where somatic pairing allows enhancers and promoters on separate chromosomes to communicate, producing expression patterns that differ from those observed when chromosomes are not paired. Transvection underscores the functional consequences of chromosome pairing for gene regulation.

Mechanistically, transvection typically involves an enhancer or other regulatory element present on one chromosome activating or repressing the promoter of the corresponding gene on the homolog. The effect depends on the two loci being in close proximity due to pairing in somatic cells and on the chromatin organization of the region. Structural rearrangements, such as inversions that separate the paired regulatory elements, can abolish or alter transvection.

Occurrences beyond Drosophila are less common but have been reported in other organisms under specific genetic contexts. Researchers use transvection to map regulatory elements and to study how chromosomal architecture shapes gene expression. The phenomenon helps distinguish cis-acting regulation from trans-acting influences and informs models of enhancer-promoter communication and sister-chromosome interactions.

Transvection remains a topic of study in chromatin biology and developmental genetics. It highlights how the physical organization of the genome in the nucleus can affect gene expression beyond the local sequence, with implications for understanding gene regulation, chromosome pairing, and the evolution of regulatory networks.