Gamete
Encyclopedia
A gamete is a cell
that fuses with another cell during fertilization (conception) in organism
s that reproduce sexually
. 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
(or egg)—and a male
produces the smaller tadpole-like type—called a sperm
. This is an example of anisogamy
or heterogamy
, 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, 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 Austria
n biologist Gregor Mendel
. Gametes carry half the genetic information of an individual, 1n
of each type.
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 pollen
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.
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 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. Additionally, base pairs in chromosomes often undergo random mutations resulting in modified DNA (and subsequently, new proteins and phenotypes). This mutation, 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
.
. They produce pollen
and ovules by meiosis, in a similar way to animals.
(of the X and Y chromosomes), whereas a sperm may carry either an X or a Y; thus the male sperm determines the sex
of any resulting zygote
, 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
.
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, 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 cell during fertilization (conception) in organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s that reproduce sexually
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
. In species that produce two morphologically distinct types of gametes, and in which each individual produces only one type, a female
Female
Female is the sex of an organism, or a part of an organism, which produces non-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 ovum
Ovum
An 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 male
Male
Male refers to the biological 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 sperm
Sperm
The 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 anisogamy
Anisogamy
Anisogamy refers to a form of sexual reproduction involving the union or fusion of two dissimilar gametes — anisogamous, anisogamic,...
or heterogamy
Heterogamy
Heterogamy 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, isogamy
Isogamy
Isogamy is a form of sexual reproduction that involves gametes of similar morphology , differing only in allele expression in one or more mating-type regions...
is the state of gametes from both sexes being the same size and shape, and given arbitrary designators for mating type
Mating type
Mating 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 Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
n biologist Gregor Mendel
Gregor Mendel
Gregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...
. Gametes carry half the genetic information of an individual, 1n
Ploidy
Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
of each type.
Sperm-egg distinction
Eggs are relatively few, large, and do not move, whereas sperm are many, small, and mobile. The size difference is mostly (but not entirely) accounted for by the very large cytoplasmCytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
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 pollen
Pollen
Pollen 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 from 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
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
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 cell
A somatic cell is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell...
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 crossover
Chromosomal crossover
Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...
(a form of genetic recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
) of chromosomes, which takes place in meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
. This hybridization has a random element, and the chromosomes tend to be a little different in every gamete that an individual produces. Additionally, base pairs in chromosomes often undergo random mutations resulting in modified DNA (and subsequently, new proteins and phenotypes). This mutation, 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
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
dissimilarity of siblings
Family
In human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...
.
Plants
Plants which reproduce sexually also have gametes, however, they are produced in the anther and ovaryOvary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
. They produce pollen
Pollen
Pollen 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 from the stamens to the pistil of flowering plants or from the male cone to the...
and ovules by meiosis, in a similar way to animals.
Sex determination
In humans, an ovum can carry only an X chromosomeX chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
(of the X and Y chromosomes), whereas a sperm may carry either an X or a Y; thus the male sperm determines the sex
Sex
In 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 zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
, 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
ZW sex-determination system
The ZW sex-determination system is a system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects , and some reptiles, including Komodo dragons...
.