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The fertile hybrids of European water frogs (genus ''Pelophylax'') reproduce by hybridogenesis (hemiclonally). This means that during gametogenesis they discard the genome of one of the parental species and produce gametes of the second parental species (containing a genome not recombined with genome of first parental species). The first parental genome is restored by fertilization of these gametes with gametes from the first species (sexual host). In all-hybrid populations of the edible frog ''Pelophylax'' kl. ''esculentus'', however, triploid hybrids provide this missing genome. Because half of the genome is transmitted to the next generation clonally (not excluded unrecombined intact genome), and only other half sexually (recombined genome of the sexual host), the hybridogenesis is a hemiclonal mode of reproduction. For example the edible frog ''Pelophylax'' kl. ''esculentus'' (mostly RL genome) which is a hybridogenetic hybrid of the marsh frog ''P. ridibundus'' (RR) and the pool frog ''P. lessonae'' (LL), usually excludes the ''lessonae'' genome (L) and generates gametes of the ''P. ridibundus'' (R). In other words, edible frogs produce gametes of marsh frogs here. The hybrid populations are propagated, however, not by the above primary hybridisations, but predominantly by backcrossess with one of the parental species they coexist (live in sympatry) with (see below in the middle). Since the hybridogenetic hybrids require another taxon as sexual host to reproduce, usually one of the parental species, they are called kleptons (with "kl." in scientific names). There are three known hybridogenetic hybrids of the European water frogs: * edible frog ''Pelophylax'' kl. ''esculentus'' (usually genotype RL): pool frog ''P. lessonae'' (LL) × ''P. ridibundus'' (RR) * Graf's hybrid frog ''Pelophylax'' kl. ''grafi'' (PR): Perez's frog ''P. perezi'' (PP) × ''P. ridibundus'' (RR) or Perez's frog ''P. perezi'' (PP) × edible frog ''P.'' kl. ''esculentus'' (RE) (it is unclear which one crossing was the primary hybridisation) * Italian edible frog ''Pelophylax'' kl. ''hispanicus'' (RB): Italian pool frog ''P. bergeri'' (BB) × ''P. ridibundus'' (RR) == Parental genome exclusion == Hybridogenesis implies that gametes of hybrids don't contain mixed parental genomes, as normally occurs by independent chromosome segregation and crossover in meiosis (see also second Mendel's law, recombination). Instead, each gamete carries a complete (haploid) genome of only one parent species. Usually one entire genome of the parental species is excluded prior to meiosis during gametogenesis, such that only one (remaining) parental genome is represented among gametes and genes from the other parent are not passed on by the hybridogen. This discarding occurs gradually during subsequent mitotic divisions, not in one step. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hybridogenesis in water frogs」の詳細全文を読む スポンサード リンク
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