Chromosome inheritance in parthenogenetic lizards and evolution of allopolyploidy in reptiles

ABOUT one percent of the 3,000 species of lizards in the world have all-female populations in which reproduction seems to be by true parthenogenesis (as opposed to gynogenesis or hybridogenesis). For some species, no males have ever been found at any localities. For a few species, all-female populations occur at some localities, bisexual populations at others. (In unisexual populations all normal individuals are females. In bisexual populations males and females normally exist.) Cytological details of oogenesis have been studied incompletely and in only a few parthenogenetic species'. The observations on Cnemidophorus (New World whiptail lizards) together with biochemical data indicating considerable fixed heterozygosity suggest that, at least for some parthenogenetic species, oogenesis normally involves an extra premeiotic endoduplication of the chromosomes, formation of "pseudobivalents" comprised of sister chromosomes, and then normal meiosis. Thus, ova usually would have the same level of ploidy as the female's typical somatic cells and would be genetically identical to each other and to the ovum from which the mother herself developed, excepting mutations (see Uzzell's review)Extensive histocompatibility between individuals of parthenogenetic species of Cnemidophorus is also consistent with this hypothesis'.