XIV.2 The next stage in the evolution of sexuality is the evolution of morphological anisogamy, differentiation of gametes into microgametes and macrogametes

If somatic cells fulfill the function of sex cells, as for unicellular organisms, then only functional differentiation of mating types usually remains.However, if the organisms form a specialized type of sex cell, gametes, for sexual reproduction, then functional anisogamy is generally followed by morphological anisogamy, differentiation of sex cells into microgametes andmacrogametes.As their names indicate, microgametes are smaller and usually mobile, while macrogametes are usually many times larger and frequently immobile.In the typical case, the microgamete contributes only its genetic material to the formation of the zygote, while the macrogamete provides both its genetic material and cytoplasm.A number of hypotheses have been formulated to explain morphological differentiation of gametes into just two types (Matsuda & Abrams 1999).

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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
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.