Biological life cycle

"The concept is closely related to those of the life history, development and ontogeny, but differs from them in stressing renewal.

Therefore, zygotic and gametic meiosis are collectively termed "haplobiontic" (single mitotic phase, not to be confused with haplontic).

Some terms (haplobiont and diplobiont) used for the description of life cycles were proposed initially for algae by Nils Svedelius, and then became used for other organisms.

[4][5] Other terms (autogamy and gamontogamy) used in protist life cycles were introduced by Karl Gottlieb Grell.

[6] The description of the complex life cycles of various organisms contributed to the disproof of the ideas of spontaneous generation in the 1840s and 1850s.

The sporophyte creates spores via meiosis which also then divide mitotically producing haploid individuals called gametophytes.

A different phenomenon, called vegetative diploidization, a type of apomixis, occurs in some brown algae (e.g., Elachista stellaris).

[22] Cells in a haploid part of the plant spontaneously duplicate their chromosomes to produce diploid tissue.

They develop to the infective larval stage in the environment, then penetrate the skin of the dog directly and mature to adults in the small intestine.

[citation needed] The primitive type of life cycle probably had haploid individuals with asexual reproduction.

The Russian biologist and historian Zhores A. Medvedev[30] considered that the accuracy of genome replicative and other synthetic systems alone cannot explain the immortality of germlines.

Rather Medvedev thought that known features of the biochemistry and genetics of sexual reproduction indicate the presence of unique information maintenance and restoration processes at the gametogenesis stage of the biological life cycle.

[30] The ancestry of each present day cell presumably traces back, in an unbroken lineage for over 3 billion years to the origin of life.

Sexual processes in eukaryotes provide an opportunity for effective repair of DNA damages in the germ line by homologous recombination.