Male

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The symbol of the Roman god Mars (god of war) is often used to represent the male sex. It also stands for the planet Mars and is the alchemical symbol for iron. Mars symbol.svg
The symbol of the Roman god Mars (god of war) is often used to represent the male sex. It also stands for the planet Mars and is the alchemical symbol for iron.

A male () organism is the physiological sex that produces the gamete known as sperm. [1] [2] [3] A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. [4] Most male mammals, including male humans, have a Y chromosome, [5] [6] which codes for the production of larger amounts of testosterone to develop male reproductive organs. Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically; however, species such as Cymothoa exigua change sex depending on the number of females present in the vicinity. [7] Male can also be used to refer to gender.

Contents

Overview

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). [8] [1] The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. [9]

Accordingly, sex is defined across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another. [1] [10] [11]

Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals; male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants.

Symbol and usage

Symbol

A common symbol used to represent the male sex is the Mars symbol ♂, a circle with an arrow pointing northeast. The Unicode code-point is:

U+2642MALE SIGN (HTML ♂ ·♂)

The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751. The symbol is sometimes seen as a stylized representation of the shield and spear of the Roman god. Mars. According to Stearn, however, this derivation is "fanciful" and all the historical evidence favours "the conclusion of the French classical scholar Claude de Saumaise (Salmasius, 15881683)" that it is derived from θρ, the contraction of a Greek name for the planet Mars, which is Thouros. [12]

Usage

In addition to its meaning in the context of biology, male can also refer to gender [13] or a shape of connectors. [14] [15]

Sex determination

Photograph of an adult male human, with an adult female for comparison. Note that both models have partially shaved body hair; e.g. clean-shaven pubic regions. Anterior view of human female and male, with labels 2.png
Photograph of an adult male human, with an adult female for comparison. Note that both models have partially shaved body hair; e.g. clean-shaven pubic regions.

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species have only two sexes (either male or female), [8] [1] [16] hermaphroditic animals, such as worms, have both male and female reproductive organs. [17]

Genetic determination

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. It is also possible in a variety of species, including humans, to be XX male or have other karyotypes. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. [18]

The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. [19] The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development; [20] for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development. [21]

The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.[ citation needed ]

Environmental determination

In some species of reptiles, such as alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. [22] In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. [23]

In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality; some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia.[ citation needed ]

Secondary sex characteristics

In those species with two sexes, males may differ from females in ways other than the production of spermatozoa.

In many insects and fish, the male is smaller than the female.

In seed plants, which exhibit alternation of generations, the female and male parts are both included within the sporophyte sex organ of a single organism.

In mammals, including humans, males are typically larger than females. [24]

In humans, males have more body hair and muscle mass. [25]

In birds, the male often exhibits a colorful plumage that attracts females. [26]

See also

Related Research Articles

Gamete Cell that fuses during fertilisation, such as a sperm or egg cell

A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that sexually reproduce. 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 produces the smaller tadpole-like type—called a sperm. In short a gamete is an egg cell or a sperm. This is an example of anisogamy or heterogamy, the condition in which females and males produce gametes of different sizes. In contrast, isogamy is the state of gametes in a species being the same size and shape, in isogamy there is no male or female sex and given arbitrary designators for mating type. The name gamete was introduced by the German cytologist Eduard Strasburger. Gametes carry half the genetic information of an individual, one ploidy of each type, and are created through meiosis.

Reproduction Biological process by which new organisms are generated from one or more parent organisms

Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.

Sex Specialization of organisms into male or female varieties

Organisms of many species are specialized into male and female varieties, each known as a sex. Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent. The gametes produced by an organism define its sex: males produce small gametes while females produce large gametes. Individual organisms which produce both male and female gametes are termed hermaphroditic. Gametes can be identical in form and function, but, in many cases, an asymmetry has evolved such that two different types of gametes (heterogametes) exist.

XY sex-determination system

The XY sex-determination system is a sex-determination system used to classify many mammals, including humans, some insects (Drosophila), some snakes, some fish (guppies), and some plants. In this system, the sex of an individual is determined by a pair of sex chromosomes. Females typically have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males typically have two different kinds of sex chromosomes (XY), and are called the heterogametic sex.

Sex-determination system A biological system that determines the development of sexual characteristics in an organism

A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. Occasionally, there are hermaphrodites in place of one or both sexes. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization.

Gonad

A gonad,sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. In the female of the species the reproductive cells are the egg cells, and in the male the reproductive cells are the sperm. The male gonad, the testicle, produces sperm in the form of spermatozoa. The female gonad, the ovary, produces egg cells. Both of these gametes are haploid cells.

Y chromosome

The Y chromosome is one of two sex chromosomes (allosomes) in mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or absence of Y that typically determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers male development. The DNA in the human Y chromosome is composed of about 59 million base pairs. The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest-evolving parts of the human genome. The human Y chromosome carries an estimated 100-200 genes, with between 45 and 73 of these protein-coding. All single-copy Y-linked genes are hemizygous except in cases of aneuploidy such as XYY syndrome or XXYY syndrome.

Sexual differentiation

Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote. Appearance of Sertoli cells in males and granulosa cells in females can be thought of as the starting point for testicular or ovarian differentiation in many species.

Testis-determining factor Protein that initiates male sex determination in therian mammals

Testis-determining factor (TDF), also known as sex-determining region Y (SRY) protein, is a DNA-binding protein encoded by the SRY gene that is responsible for the initiation of male sex determination in therian mammals. SRY is an intronless sex-determining gene on the Y chromosome. Mutations in this gene lead to a range of disorders of sex development (DSD) with varying effects on an individual's phenotype and genotype.

Anisogamy Sexual reproduction involving a large, "female" gamete and a small, "male" gamete

Anisogamy is the form of sexual reproduction that involves the union or fusion of two gametes, which differ in size and/or form. The smaller gamete is considered to be male, whereas the larger gamete is regarded as female.

Isogamy

Isogamy is a form of sexual reproduction that involves gametes of similar morphology, differing in general only in allele expression in one or more mating-type regions. Because both gametes look alike, they cannot be classified as "male" or "female". Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as "+" and "−" strains, although in some species of Basidiomycota there are more than two mating types, some can even have thousands of mating types. In all cases, fertilization occurs when gametes of two different mating types fuse to form a zygote.

Sexual characteristics are physical or behavioral traits of an organism which are indicative of its biological sex. These can include sex organs used for reproduction and secondary sex characteristics which distinguish the sexes of a species, but which are not directly part of the reproductive system.

Gametogonium are stem cells for gametes located within the gonads. They originate from primordial germ cells, which have migrated to the gonads. Male gametogonia which are located within the testes during development and adulthood are called spermatogonium. Female gametogonia, known as oogonium, are found within the ovaries of the developing foetus and were thought to be depleted at or after birth. Spermatogonia and oogonia are classified as sexually differentiated germ cells.

X0 sex-determination system

The X0 sex-determination system determines the sex of offspring among:

Sex chromosome

A sex chromosome, is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical pair of mammal allosomes, determine the sex of an individual created in sexual reproduction. Autosomes differ from allosomes because autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex.

Sexual differentiation in humans The process of development of sex differences in humans

Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. Sexual differentiation includes development of different genitalia and the internal genital tracts and body hair plays a role in gender identification.

Hermaphrodite An organism that has complete or partial male and female reproductive organs

In reproductive biology, a hermaphrodite is an organism that has complete or partial reproductive organs and produces gametes normally associated with both male and female sexes. Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the "female" or "male". For example, the great majority of tunicates, pulmonate snails, opisthobranch snails, earthworms, and slugs are hermaphrodites. Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. Most plants are also hermaphrodites.

Female The sex of an organism which produces ova

Female is the sex of an organism, or a part of an organism, that produces non-mobile ova. Barring rare medical conditions, most female mammals, including female humans, have two X chromosomes. Female characteristics vary between different species with some species containing more well defined female characteristics, such as the presence of pronounced mammary glands. There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages.

Sexual reproduction Reproduction process that creates a new organism by combining the genetic material of two organisms

Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete with a single set of chromosomes (haploid) combines with another to produce an organism composed of cells with two sets of chromosomes (diploid). Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. Sexual reproduction does not occur in prokaryotes, but they have processes with similar effects such as bacterial conjugation, transformation and transduction, which may have been precursors to sexual reproduction in early eukaryotes.

Gynogenesis, a form of parthenogenesis, is a system of asexual reproduction that requires the presence of sperm without the actual contribution of its DNA for completion. The paternal DNA dissolves or is destroyed before it can fuse with the egg. The egg cell of the organism is able to develop, unfertilized, into an adult using only maternal genetic material. Gynogenesis is often termed “sperm parasitism” in reference to the somewhat pointless role of male gametes. Gynogenetic species, "gynogens" for short, are unisexual, meaning they must mate with males from a closely related bisexual species that normally reproduces sexually. It’s a disadvantageous mating system for males, as they are unable to pass on their DNA. The question as to why this reproductive mode exists, given that it appears to combine the disadvantages of both asexual and sexual reproduction, remains unsolved in the field of evolutionary biology.

References

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Further reading