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Biological life cycle

A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction.

In regard to its ploidy, there are three types of cycles; haplontic life cycle, diplontic life cycle, diplobiontic life cycle.

These three types of cycles feature alternating haploid and diploid phases (n and 2n).

The haploid organism becomes diploid through fertilization, which joins of gametes.

This results in a zygote which then germinates.

To return to a haploid stage, meiosis must occur.

The cycles differ in the product of meiosis, and whether mitosis (growth) occurs.

Zygotic and gametic meioses have one mitotic stage and form: during the n phase in zygotic meiosis and during the 2n phase in gametic meiosis.

Therefore, zygotic and gametic meiosis are collectively term haplobiontic (single mitosis per phase).

Sporic meiosis, on the other hand, has two mitosis events (diplobiontic): one in each phase.

Note:   The above text is excerpted from the Wikipedia article "Biological life cycle", which has been released under the GNU Free Documentation License.
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