The study of hybridogenesis is expected to shed light on the role played by the so-called ‘asexual reproduction’ in vertebrate evolution, since hybridogenesis, gynogenesis and parthenogenesis are restricted to lower vertebrates. Hence, it seemed interesting to define the stage and time of germline differentiation in reproductively unstable organisms which, to accomplish functional gamete maturation, can change the normal approach to meiosis by means of unusual cytological steps, such as genome elimination and endoreduplication. The cytogenetic aspects of ‘asexual’ meiosis have already been thoroughly studied. At present, molecular investigations are in progress to characterise the single steps of germline differentiation in a hybridogenetic green frog system, and the results obtained so far can be considered promising, as shown in this work. Vasa, PL10 and Y-box homolog genes, first isolated in Rana (Pelophylax), are expressed during early phases of gametogenesis in R. (P.) ridibunda and R. (P.) lessonae (parental species), and R. (P.) esculenta (their natural hybrid), suggesting that gametogenesis, during the adult life, follows a unique genetic sequence in the two parental species as well as in hybridogenetic hybrids. Similar molecular investigations need to be carried out on larval stages prior to metamorphosis, when the genetic plasticity of gemline cells allows their commitment versus either the standard and/or hybridogenetic reproduction mode.
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