Cnemidophorus is a genus of lizards which belong to the family of Teiidae, which are commonly referred to as whiptail lizards or racerunners. Note that the nomenclature for this genus has recently been re-examined by T. W. Reeder et al. in 2002. Many species that were Cnemidophorus should now likely be considered Aspidoscelis based upon divergent characters between the two groups.

In some of the Cnemidophorus species, there are no males, and they reproduce through parthenogenesis. This is well-known in bees and aphids, but is very rare in vertebrates. Those species without males are now known to originate through hybridization, or interspecific breeding. Occasionally, a mating between a female of one species and a male of another produces a parthenogen, a female that is able to produce viable eggs that are genetically identical to her own cells. The lizards that hatch from these eggs are thus also parthenogens that can again produce identical eggs, resulting in an asexual, clonal population. Parthenogenetic species resulting from a single hybridization are diploid (that is, they have two sets of chromosomes just as sexual species do), but sometimes these females mate with other males, producing offspring which are triploid (that is, they have three sets of chromosomes, or 50% more than equivalent sexual species; see polyploidy). Over 30% of the Cnemidophorus genus are parthenogenic.