From Encyclopedia Jr, free information reference for Kids
A gamete is a specialized germ cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. In species which produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female is any individual which produces the larger type of gamete -- called an ovum (or egg) — and a male produces the smaller type — called a spermatozoon (or sperm cell) in animals, and a pollen grain in higher plants.
The creation of gametes is called gametogenesis, and during it gametocytes divide by meiosis into gametes. Organs that produce gametes are called gonads in animals, and archegonia or antheridia in plants. The term gamete comes from the ancient Greek γαμετης (spouse).
Gametes are haploid cells; that is, they contain one complete set of chromosomes (the actual number varies from species to species). When two gametes fuse (in animals typically involving a sperm and an egg), they form a zygote — a cell that has two complete sets of chromosomes and therefore is diploid. The zygote receives one set of chromosomes from each of the two gametes through the fusion of the two gamete nuclei. After multiple cell divisions and cellular differentiation, a zygote develops, first into an embryo, and ultimately into a mature individual capable of producing gametes. Gametes from a mature diploid individual are produced in the gonadal tissue through meiosis —a process of cellular division that reduces the number of sets of chromosomes from two to one (i.e., produces haploid gametes).
The diploid somatic cells of an individual contains one copy of the chromosome set from the sperm and one copy of the chromosome set from the egg; that is, the cells of the offspring have genes expressing characteristics of both the father and the mother. A gamete's chromosomes are not exact duplicates of either of the sets of chromosomes carried in the somatic cells of the individual that produced the gametes. They can be hybrids produced through crossover (a form of genetic recombination) of chromosomes, which takes place in meiosis. This hybridization has a random element, and the chromosomes tend to be a little different in every gamete that an individual produces. This recombination and the fact that the two chromosome sets ultimately come from either a grandmother or a grandfather on each parental side account for the genetic dissimilarity of siblings.
Isogamy is the state of gametes from both sexes being the same size. Anisogamy or heterogamy is the condition wherein females and males produce gametes of different sizes.
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