The alternation of the two phases of life cycle between sexual phase and asexual phase is called alternation of generation. Such life cycle pattern is commonly observed in plants and algae. It is also called metagenesis and in it haploid gametophytic (generally sexual) generation alternates with diploid sporophytic (generally asexual) generation.

There are three variations in the life cycle. In diplontic life cycle, the sporophyte is diploid, dominant, autotrophic and independent. The gametophytic generation is haploid, recessive and dependent on sporophyte. The duration of sporophyte is longer than gametophyte generation. Observed in Angiosperms.

In haplontic life cycle, the gametophyte stage is dominant, green, haploid and independent while the sporophyte stage is diploid, recessive and partially dependent on gametophyte. Also, the gametophytic stage duration is longer than the sporophytic stage. Observed in algae.

In haplodiplontic life cycle, both the stages have nearly equal duration and none of them are dominant. Gametophyte is represented as independent, autotrophic and haploid. Whereas the sporophyte is independent, autotrophic and diploid. Pteridophytes show such life cycle.