Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

At a certain stage in sexual reproduction, fusion, i.e. syngamy, occurs of two sex cells bearing a single copy of the genome, i.e. two haploid gametes. The newly formed zygote is then necessarily diploid and, prior to entering the normal asexual cell cycle, can either renew its haploid state and further cyclically alternate between the haploid (in the G₁-phase) and diploid (in the G₂-phase) states, or can remain diploid and alternate between the diploid state (in the G₁-phase) and the tetraploid state (in the G₂-phase) for the time of its sexual reproduction. It is necessary to state that the ploidy of the cells is even greater in a great many differentiated tissues of multicellular organisms.