A gamete (; , ultimately ) is a
haploid cell that fuses with another haploid cell during
fertilization in
organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...
s that
reproduce sexually.
Gametes are an organism's reproductive cells, also referred to as sex cells.
In species that produce two
morphologically distinct types of gametes, and in which each individual produces only one type, a
female is any individual that produces the larger type of gamete—called an
ovum— and a
male
Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization.
A male organism cannot reproduce sexually without access to ...
produces the smaller type—called a
sperm. Sperm cells or spermatozoa are small and motile due to the flagellum, a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell or ovum is relatively large and non-motile.
In short a gamete is an egg cell (female gamete) or a sperm (male gamete). In animals, ova mature in the ovaries of females and sperm develop in the testes of males. During fertilization, a spermatozoon and ovum unite to form a new
diploid organism
In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...
.
Gametes carry half the
genetic information
A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are u ...
of an individual, one
ploidy of each type, and are created through
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...
, in which a germ cell undergoes two fissions, resulting in the production of four gametes.
In biology, the type of gamete an organism produces determines the classification of its sex.
This is an example of
anisogamy or
heterogamy, the condition in which females and males produce gametes of different sizes (this is the case in humans; the human ovum has approximately 100,000 times the volume of a single human sperm cell). In contrast,
isogamy is the state of gametes from both sexes being the same size and shape, and given arbitrary designators for
mating type. The name gamete was introduced by the German cytologist
Eduard Strasburger. Male and female gametes set the basis for the sexual roles and sexual selection.
Oogenesis is the process of female gamete formation in animals. This process involves
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...
(including
meiotic recombination) occurring in the diploid primary
oocyte to produce the haploid
ovum.
Spermatogenesis is the process of male gamete formation in animals. This process also involves meiosis occurring in the diploid primary
spermatocyte to produce the haploid
spermatozoon.
Evolution
It is generally accepted that
isogamy is the ancestral state from which
anisogamy evolved, although its evolution has left no fossil records.
Oogamy also evolved from isogamy through anisogamy. There are almost invariably only two gamete types, all analyses showing that intermediate gamete sizes are eliminated due to selection.
Intermediate sized gametes do not have the same advantages as small or large ones; they do worse than small ones in mobility and numbers, and worse than large ones in supply.
Dissimilarity
In contrast to a gamete, a diploid
somatic cell of an individual contains one copy of the
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
set from the sperm and one copy of the chromosome set from the egg cell. Consequently, the cells of the offspring have genes potentially capable of expressing characteristics of both the ''father'' and the ''mother'', subject to whether they are
dominant or recessive. A gamete's chromosomes are not exact duplicates of either of the sets of chromosomes carried in the diploid chromosomes but a mixture of the two.
Sex determination in mammals and birds
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and most mammals use the
XY sex-determination system in which a normal ovum can carry only an
X chromosome whereas a sperm may carry either an X or a Y, while a non-normal sperm cell can end up carrying either no sex-defining chromosomes, an XY pair, or an XX pair; thus the male sperm determines the
sex of any resulting
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicell ...
. If the zygote has two X chromosomes it will develop into a female, if it has an X and a Y chromosome, it will develop into a male.
For birds, the female ovum determines the sex of the offspring, through the
ZW sex-determination system.
Artificial gametes
Artificial gametes, also known as In vitro derived gametes (IVD), stem cell-derived gametes (SCDGs), and In vitro generated gametes (IVG), are gametes derived from
stem cells. The use of such artificial gametes would
UOTE:"necessarily require
IVF techniques".
Research shows that artificial gametes may be a reproductive technique for same-sex male couples, although a
surrogate mother would still be required for the gestation period.
Women who have passed
menopause may be able to produce eggs and bear genetically related children with artificial gametes.
Robert Sparrow wrote, in the
Journal of Medical Ethics, that embryos derived from artificial gametes could be used to derive new gametes and this process could be repeated to create multiple human generations in the laboratory.
This technique could be used to create
cell lines for medical applications and for studying the heredity of
genetic disorders.
Additionally, this technique could be used for
human enhancement by
selectively breeding for a desired genome or by using
recombinant DNA
Recombinant DNA (rDNA) molecules are DNA molecules formed by laboratory methods of genetic recombination (such as molecular cloning) that bring together genetic material from multiple sources, creating sequences that would not otherwise be f ...
technology to create enhancements that have not arisen in nature.
Plants
Plants which reproduce sexually also produce gametes. However, since plants have a life cycle involving
alternation of diploid and haploid generations some differences exist. Plants use
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...
to produce spores that develop into
multicellular
A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism.
All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially ...
haploid
gametophytes which produce gametes by mitosis. The sperm are formed in an organ known as the
antheridium and the egg cells in a flask-shaped organ called the
archegonium. In
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants t ...
s, the female gametophyte is produced inside the
ovule within the
ovary of the flower. When mature, the haploid gametophyte produces female gametes which are ready for fertilization. The male gametophyte is produced inside a
pollen grain within the
anther. When a pollen grain lands on a mature
stigma of a flower it germinates to form a
pollen tube that grows down the style into the ovary of the flower and then into the ovule. The pollen then produces sperm by mitosis and releases them for fertilization.
See also
*
Coenogamete A coenogamete is a multi-nucleate gamete (a gamete with more than one nucleus). Fusion of coengametes creates Coenocytes.
They exist amongst members of the phylum Porifera (sponges) under kingdom Animalia and division Zygomycota of kingdom Fungi
...
Notes and references
{{Authority control
Classical genetics
Germ cells
Reproductive system