Alternation of Generations

Alternation of Generations

The cells of most plants and animals have two sets of chromosomes and only their reproductive cells (gametes) have just one set. In Bryophytes the main plant is the gametophyte stage and its cells have only one set of chromosomes. When a Moss sperm fertilises an egg, the number of chromosomes is doubled and cells of the sporophyte (capsule and seta) have two sets. When spores are formed, the number of chromosomes is halved again. So Bryophytes show a clear alternation of gametophyte and sporophyte generations that is not obvious in most higher plants, in which the gametophyte generation is greatly reduced. [CH] {ML}