Alternation of Generations

Sexual reproduction involves the two alternating processes of meiosis and fertilization. Whatever variation in details there may be from one organism to another, these two activities must occur alternately if sexual reproduction is to continue.

In animals, meiosis generates the haploid gametes — sperm and eggs — directly. These single cells fuse to form the zygote which will develop into another diploid animal.

In most plants meiosis and fertilization divide the life of the organism into two distinct phases or "generations".

Two points revealed by plant life cycles:

In fact, the gametophyte generation is the major stage in the life of mosses and an independent plant in ferns.

Links to descriptions of the gametophytes of mosses and of ferns.

However, the gametophyte is only an inconspicuous structure in angiosperms and other "higher" plants.

Link to illustrated discussion of the gametophyte generation in angiosperms.
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21 December 2010