Gametophyte

gametophyte (gəmē`təfīt'), phase of plant life cycles in which the gametes, i.e., egg and sperm, are produced. The gametophyte is haploid, that is, each cell contains a single complete set of chromosomes, and arises from the germination of a haploid spore. In many lower plants, the gametophyte phase is the dominant plant form; for example, the familiar mosses are the gametophyte form of the plants. The alternate phase of the plant life cycle is the sporophyte, the diploid plant form, with each cell containing two complete sets of chromosomes. For example, in mosses the sporophyte is a capsule atop a slender stalk that grows out of the top of the gametophyte. The sporophyte develops from the union of two gametes, such as an egg fertilized by a sperm; in turn, the sporophyte forms spores that develop into gametophytes. The alternation between haploid gametophyte and diploid sporophyte phases, known as alternation of generations, occurs in all multicellular plants. As plants advanced in evolutionary development, the sporophyte became the increasingly dominant plant form and the gametophyte form has been correspondingly reduced. In contrast to mosses, for example, in the advanced angiosperms the male and female gametophytes are reduced to three-celled and seven-celled structures, respectively, found within the reproductive organs of the familiar flowering plant (the sporophyte). See also fertilization; reproduction.

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gametophyte

In certain plants, the sexual phase (or an individual representing the phase) in the alternation of generations. The alternate, nonsexual phase is the sporophyte. In the gametophyte phase, male and female organs (gametangia) develop and produce eggs and sperm (gametes), which unite in fertilization (syngamy). The fertilized egg (zygote) develops into the sporophyte, which produces numerous single-celled spores, which in turn develop directly into new gametes.

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gametophyte [gə′mēd·ə‚fīt]

(botany)

The haploid generation producing gametes in plants exhibiting metagenesis.

An individual plant of this generation.

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Gametophyte 

sexual generation in those plants that exhibit alternation of generations. The gametophyte alternates in the development cycle with the asexual generation or sporophyte. In many plants the gametophyte carries on an autonomous existence, independent of the sporophyte. In some cases it is not distinguishable from the sporophyte by its external appearance (for example, the gametophyte in many algae); in others it is very distinct, for example, in the prothallia of ferns, horsetails, and lycopodia. In angiospermous plants the gametophyte is reduced to a pollen grain (male gametophyte) and to an embryo sac (female gametophyte). The gametophyte cell nuclei are characterized by half the number (haploid) of chromosomes in comparison to the cell nuclei of the sporophyte.