gametofyyttien

Gametophytes are the haploid, multicellular stages in the life cycle of many plants and some algae that produce gametes by mitosis. In plants, life cycles often show alternating generations, with the sporophyte (diploid) producing haploid spores by meiosis, which then germinate into gametophytes. These gametophytes generate gametes—sperm and eggs—through mitotic cell division, and fusion of these gametes during fertilization restores the diploid state in the zygote.

Gametophytes bear gametangia, organized structures that produce gametes. In many groups, antheridia generate sperm and archegonia produce eggs. In bryophytes (mosses, liverworts, hornworts) the gametophyte is the dominant, free-living form, while the sporophyte is often smaller and dependent on the gametophyte for nutrition.

In vascular plants, including ferns and seed plants, the sporophyte is the dominant life stage, and the gametophyte is typically reduced and nutritionally dependent on the sporophyte. In seed plants, the male gametophyte is the pollen grain, while the female gametophyte is the embryo sac contained within the ovule. Fertilization in these groups is typically pollen-mediated and does not require free-standing water for the sperm to reach the egg.

The transition from the gametophyte to the sporophyte marks the beginning of a new generation. In many species, the two generations differ markedly in size, morphology, and ecology, contributing to the diversity of plant forms. Gametophytes thus play a central role in plant reproduction and evolutionary history by mediating haploid processes and genetic variation through sexual reproduction.