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[6] [7] [8] There are almost invariably only two gamete types, all analyses showing that intermediate gamete sizes are eliminated due to selection. [9] [10] Since intermediate sized gametes do not have the same advantages as small or large ones, [11] they do worse than small ones in mobility and numbers, and worse than large ones in supply. [12]
Some cells in other animals may be flagellate, for instance the spermatozoa of most animal phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, and some gymnosperms and closely related plants do so. [2] Likewise, most fungi do not produce cells with flagellae, but the primitive fungal chytrids do. [3]
The range is the northeast Atlantic Ocean (including the Baltic and North Seas), from the North Cape, Norway and the Kola Peninsula south to central Portugal. [6] [7]Laminaria hyperborea grows on rocks in the sublittoral zone at depths down to about 10 m (35 ft) in turbid waters and down to 30 m (100 ft) where the water is clear. [8]
Gametes are produced within the gonads through a process known as gametogenesis. This occurs when certain types of germ cells undergo meiosis to split the normal diploid number of chromosomes (n=46) into haploid cells containing only 23 chromosomes. [10] Anatomy of the testis
For example, some brown alga (Phaeophyceae) reproduce by producing multi-flagellated male and female gametes that recombine to form the diploid sporangia. [2] Zoids are primarily found in some protists, diatoms, [1] green alga, brown alga, [3] non-vascular plants, [4] and a few vascular plants (ferns, [1] cycads, [5] and Ginkgo biloba [6]).
The list of organisms by chromosome count describes ploidy or numbers of chromosomes in the cells of various plants, animals, protists, and other living organisms.This number, along with the visual appearance of the chromosome, is known as the karyotype, [1] [2] [3] and can be found by looking at the chromosomes through a microscope.
Anisogamy is the form of sexual reproduction that involves the union or fusion of two gametes which differ in size and/or form. [12] The smaller gamete is considered to be male (a sperm cell), whereas the larger gamete is regarded as female (typically an egg cell, if non-motile).
Note 1] Some isogamous species have more than two mating types, but the number is usually lower than ten. In some extremely rare cases, such as in some basidiomycete species, a species can have thousands of mating types. [7] Under the strict definition of isogamy, fertilization occurs when two gametes fuse to form a zygote. [8]