Hybrizyme

Hybrizyme is a term coined to indicate novel or normally rare gene variants that are associated with hybrid zones, geographic areas where two related taxa meet, mate, and produce hybrid offspring. The hybrizyme phenomenon is widespread and these alleles occur commonly, if not in all hybrid zones. Initially considered to be caused by elevated rates of mutation in hybrids, the most probable hypothesis infers that they are the result of negative (purifying) selection. Namely, in the center of the hybrid zone, negative selection purges alleles against hybrid disadvantage. Stated differently, any allele that will decrease reproductive isolation is favored and any linked alleles also increase their frequency by genetic hitchhiking. If the linked alleles used to be rare variants in the parental taxa, they will become more common in the area where the hybrids are formed.

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