What is "hybrizyme"

Hybrizyme is a term coined to indicate novel or normally rare gene variants (or alleles) that are associated with hybrid zones, geographic areas where two related species meet, mate, and produce hybrid offspring. Hybrizymes occur commonly in many, if not all, hybrid zones. Originally considered to be caused by elevated rates of mutation in hybrids, they are now believed to be the result of purifying selection: in the centre of the hybrid zone, alleles for hybrid fitness are selected, and linked alleles also increase in frequency by genetic hitchhiking. If those linked alleles happen to be rare variants, they will become more common, and their commonness will only be associated with the area where hybrids are formed.