A
gamete (from
Ancient GreekAncient Greek is the historical stage in the development of the Greek language spanning across the Archaic , Classical , and Hellenistic periods of ancient Greece and the ancient world. It is predated in the 2nd millennium BC by Mycenaean Greek...
γαμέτης; translated
gamete = wife,
gametes = husband) is a
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
that fuses with another gamete during fertilization (conception) in
organismIn biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
s that
reproduce sexuallySexual reproduction is characterized by processes that pass a combination of genetic material to offspring, resulting in diversity. The main two processes are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the restoration...
. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a
femaleFemale is the sex of an organism, or a part of an organism, which produces mobile ova .- Defining Characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
is any individual that produces the larger type of gamete — called an
ovumAn ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
(or egg) — and a
maleMale refers to the sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
produces the smaller tadpole-like type — called a
spermThe term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
. This is an example of
anisogamyAnisogamy refers to a form of sexual reproduction involving gametes of different sizes. The smaller gamete is considered to be male , whereas the larger gamete is regarded as female ....
or
heterogamyHeterogamy has a number of biological definitions:*In reproductive biology, heterogamy is the alternation of differently organized generations, applied to the alternation between parthenogenetic and a sexual generation...
, the condition wherein females and males produce gametes of different sizes (this is the case in humans; the human ovum is approximately 20 times larger than the human sperm cell). In contrast,
isogamyIsogamy refers to a form of sexual reproduction involving gametes of similar morphology, differing only in allele expression in one or more mating-type regions. Since both gametes look alike, they cannot be classified as "male" or "female." Instead, organisms undergoing isogamy are said to have...
is the state of gametes from both sexes being the same size and shape, and given arbitrary designators for
mating typeMating types occur in eukaryotes that undergo sexual reproduction via isogamy. Since the gametes of different mating types look alike, they are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female." Mating can only take place between different mating...
.
The name gamete was introduced by the
AustriaAustria , officially the Republic of Austria , is a landlocked country of roughly 8.3 million people in Central Europe. It borders both Germany and the Czech Republic to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the west...
n biologist
Gregor MendelGregor Johann Mendel was an Augustinian priest and scientist, and is often called the father of genetics for his study of the inheritance of certain traits in pea plants. Mendel showed that the inheritance of these traits follows particular laws, which were later named after him...
. Gametes carry half the genetic information of an individual, one
chromosomeA chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions...
of each type. In humans, an ovum can carry only
X chromosomeThe X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals . It is a part of the XY sex-determination system and X0 sex-determination system...
(of the X and Y chromosomes), whereas a sperm can carry either an X or a Y; hence, it has been suggested that males have the control of the
sexIn biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
of any resulting
zygoteA zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development...
, as the
genotypeThe genotype is the genetic constitution of a cell, an organism, or an individual usually with reference to a specific character under consideration...
of the sex-determining chromosomes of a male must be XY and a female XX. In other words, due to the presence of the Y chromosome exclusively in the sperm, it is that gamete alone that can determine that an offspring will be a male.
Gametogenesis
The production of gameotypes is termed
gametogenesis, during which phase
gametocyteA gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called spermatocytes, and female gametocytes are called oocytes....
s divide by
meiosisIn biology, meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original...
into gametes. Meiosis reduces the number of sets of chromosomes from two to one (i.e., produces haploid gametes from diploid gametocytes). Organs that produce gametes are called
gonadThe gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s in animals, and
archegoniaAn archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants producing and containing the ovum or female gamete. The archegonium has a long neck and a swollen base...
or
antheridiaAn antheridium is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
in plants.
Gamete cycle
A gamete of two generation ultimately creates a gamete in the next generation, but still keeping the same quantity of genetic information.
Gametes are haploid cells; that is, they contain half(n) of a complete set of
chromosomeA chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions...
s (the actual number varies from species to species). When two gametes fuse (in animals typically involving a sperm and an egg), they form a
zygoteA zygote , or zygocyte, is the initial cell formed when a new organism is produced by means of sexual reproduction. A zygote is synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development...
—a cell that has a complete set of chromosomes(2n) and therefore is diploid. The zygote receives one set of chromosomes from each of the two gametes through the fusion of the two gamete
nucleiIn cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as...
. After multiple
cell divisionCell division is a process by which a cell, called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing...
s and
cellular differentiationIn developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of...
, a zygote
developsDevelopmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy.Developmental biology is that...
, first into an
embryoAn embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
, and ultimately into a mature individual capable of producing gametes.
Sperm-egg distinction
Eggs are relatively few, large, and immobile, whereas sperm are many, small, and mobile. The size difference is mostly (but not entirely) accounted for by the very large
cytoplasmThe cytoplasm is the part of a cell that is enclosed within the cell membrane. In eukaryotic cells, the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes. The contents of the cell nucleus...
of the egg. Eggs awaiting zygote formation may be anchored either to something in the environment or by an organ that contains them; sperm may rely solely on their own motility or may be relayed into place by an organ such as
pollenPollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement between the stamens to the pistil of flowering plants or from the male cone to the...
to reach the place of zygote formation. Typically many more sperm than eggs are created and wasted, in the sense of never fusing with a partner gamete.
The sperm/egg distinction is the basis for distinguishing between males and females. Since some algae and fungi have sexual reproduction by combining two identical gametes, there is no male/female distinction in these species. This raises the question as to why most large/familiar species reproduce by sperm and egg. One theory for why the male/female distinction is so common is that it facilitated encounters between gametes, in ancestral marine species.
Dissimilarity
In contrast to a gamete, the diploid
somatic cellSomatic cells are any cells forming the body of an organism, as opposed to germline cells. In mammals, germline cells are the spermatozoa and ova which fuse during fertilization to produce a cell called a zygote, from which the entire mammalian embryo develops...
s of an individual contain 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
crossoverChromosomal crossover is the exchange of genetic material between homologous chromosomes. This often occurs during prophase 1 of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed until near the end of prophase 1...
(a form of
genetic recombinationGenetic recombination is the process by which a strand of genetic material is broken and then joined to a different DNA molecule. In eukaryotes recombination occurs in mitosis as a common mechanism of DNA repair and in meiosis as a way of facilitating chromosomal crossover...
) 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
geneticGenetics, , a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding...
dissimilarity of
siblingsFamily denotes a group of people or animals affiliated by a consanguinity, affinity or co-residence...
.