gametophyte
Americannoun
noun
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Among organisms which display an alternation of generations as part of their life cycle (such as plants and certain algae), the haploid organism that produces gametes. Each of its cells has only one, unpaired set of chromosomes, as opposed to the corresponding diploid form of the organism, called the sporophyte. A gametophyte develops from spores produced by the sporophyte. The gametophytes of homosporous plants are bisexual (produce both eggs and sperm), while the gametophytes of heterosporous plants, such as all seeds plants, are unisexual (produce only eggs or only sperm).
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See more at alternation of generations sporophyte
Closer Look
The evolution of plants has seen a steady reduction in the independence and size of the gametophyte generation when compared to the sporophyte generation. In the more primitive nonvascular plants, such as the mosses and liverworts, the gametophyte is the main plant form. It is relatively large and not dependent on the sporophyte for nutrition. In some species, the gametophytes are bisexual; in others, the sexes are separate. Female gametes remain in the gametophyte, where they are fertilized by sperm, usually from another gametophyte. The resultant embryos develop into sporophytes. These grow as smaller plants in or upon the gametophytes. The diploid sporophytes then produce haploid spores by meiosis, and these are dispersed and grow into new gametophytes. Among the vascular plants, however, the sporophyte is the larger plant form. For example, the familiar pine tree represents the diploid sporophyte generation. By meiosis, the pine eventually produces male and female gametophytes. The male gametophytes of the pine are small—they are the pollen grains released by male cones to be dispersed to female cones. The larger female gametophytes remain within the ovules of the female cones of the pine and are dependent on the surrounding sporophyte tissues for their nutrition. Each female gametophyte develops two egg cells, both of which are fertilized by a male gamete from a pollen grain. However, usually only one embryo will complete its development. This embryo is a new diploid sporophyte, housed within the developing pine seed. A pine seed thus contains three generations of the pine plant: the seed coat that arises from diploid tissue belonging to the ovule, the haploid gametophyte tissue that will serve as a food reserve for the embryo after germination, and the diploid embryo itself. In angiosperms, the female gametophyte has evolved into an even more reduced form. It consists of only the seven cells of the embryo sac.
Other Word Forms
- gametophytic adjective
Etymology
Origin of gametophyte
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Example Sentences
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Most plants exhibit alternation of generations, which is described as haplodiplodontic: the haploid multicellular form, known as a gametophyte, is followed in the development sequence by a multicellular diploid organism: the sporophyte.
From Textbooks • Jan. 1, 2015
The short, blue-green gametophyte is the dominant phase of the lifecycle of a hornwort.
From Textbooks • Jan. 1, 2015
The haploid gametophyte alternates with the diploid sporophyte during the sexual reproduction process of angiosperms.
From Textbooks • Jan. 1, 2015
During the second phase, megagametogenesis, the surviving haploid megaspore undergoes mitosis to produce an eight-nucleate, seven-cell female gametophyte, also known as the megagametophyte or embryo sac.
From Textbooks • Jan. 1, 2015
Thus in Pellia the nuclei of the gametophyte have eight chromosomes and those of the sporophyte sixteen.
From Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria" by Various
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
