Alteration of generation is a reproductive cycle and method of growth of certain species. It is found in both the animal and plant kingdoms although it is more common with certain plant species. It is characterized by the haploid phase (which reproduces sexually) alternating with the diploid phase (which reproduces asexually).

In mosses and vascular plants there is a sexual and an asexual phase. The haploid (sexual) phase involves gametophyte (gamete or sperm cell plant) generation; the diploid (asexual) phase involves sporophyte (spore plant) generation.

The cycle begins with a sexually mature plant which is capable of producing egg and sperm cells. Both egg and sperm, as well as the parent plant, are haploid. The egg and sperm fuse to produce a diploid zygote. The zygote (a cell formed by the union of male and female gametes) does not immediately grow into a new...