Alternation of the ploidy phases of the life cycle in multicellular organisms is called metagenesis. Very frequently the two ploidy phases differ in their means of reproduction, where the haploid gametophytes form gametes and the diploid sporophytes form spores. In some organisms, the gametophyte phase is more important, i.e. larger, morphologically more complicated and longer-lasting (mosses and lichens); in others, the sporophyte phase predominates (angiosperm plants), while the two phases do not much differ in other organisms (ferns,  Pteridophyta) (Jenkins 1993; Mable & Otto 1998). Alternation of phases with sexual and nonsexual reproduction also occurs in some animals (especially Turbellaria and Cnidaria). This process is also designated as metagenesis in this case, although the bodies of both the  sexual and nonsexual phases are composed of diploid cells under these circumstances.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more