The
XY sex-determination system is the
sex-determination systemA sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual...
found in
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s, most other
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s, some insects (
DrosophilaDrosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
) and some plants (
GinkgoGinkgo , also known as the Maidenhair Tree after Adiantum, is a unique species of tree with no close living relatives...
). In this system, females have two of the same kind of
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...
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...
(XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.
The XY sex determination system was first described independently by
Nettie StevensNettie Maria Stevens was an early American geneticist. She and Edmund Beecher Wilson were the first researchers to describe the chromosomal basis of sex....
and
Edmund Beecher WilsonEdmund Beecher Wilson was a pioneering American zoologist and geneticist.Wilson was born in Geneva, Illinois, and graduated from Yale in 1878. He earned his doctorate at Johns Hopkins in 1881....
in 1905.
Some species (including most mammals) have a
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
or genes on the
Y chromosomeThe Y chromosome is the sex-determining chromosome in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development, thus determining sex. The human Y chromosome is composed of about 60 million base pairs.- Overview :...
that determine maleness.
The
XY sex-determination system is the
sex-determination systemA sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual...
found in
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s, most other
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s, some insects (
DrosophilaDrosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
) and some plants (
GinkgoGinkgo , also known as the Maidenhair Tree after Adiantum, is a unique species of tree with no close living relatives...
). In this system, females have two of the same kind of
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...
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...
(XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.
The XY sex determination system was first described independently by
Nettie StevensNettie Maria Stevens was an early American geneticist. She and Edmund Beecher Wilson were the first researchers to describe the chromosomal basis of sex....
and
Edmund Beecher WilsonEdmund Beecher Wilson was a pioneering American zoologist and geneticist.Wilson was born in Geneva, Illinois, and graduated from Yale in 1878. He earned his doctorate at Johns Hopkins in 1881....
in 1905.
Mechanisms
Some species (including most mammals) have a
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
or genes on the
Y chromosomeThe Y chromosome is the sex-determining chromosome in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development, thus determining sex. The human Y chromosome is composed of about 60 million base pairs.- Overview :...
that determine maleness. In the case of humans, a single gene (
SRYSRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the high mobility group -box family of DNA-binding proteins...
) on the Y chromosome acts as a signal to set the developmental pathway towards maleness. Other mammals use several genes on the Y chromosome for that same purpose. Not all male-specific genes are located on the Y chromosome.
Other species (including most
DrosophilaDrosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
species) use the presence of two
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...
s to determine femaleness. One X chromosome gives putative maleness. The presence of Y chromosome genes is required for normal male development.
Humans, as well as some other organisms, can have a chromosomal arrangement that is contrary to their phenotypic sex, that is, XX males or XY females. See, for example,
XX male syndromeXX male syndrome is a rare sex chromosomal disorder. Usually it is caused by unequal crossing over between X and Y chromosomes during meiosis....
and
Androgen insensitivity syndromeAndrogen insensitivity syndrome , also referred to as androgen resistance syndrome, is a set of disorders of sex development caused by mutations of the gene encoding the androgen receptor. The nature of the resulting problem varies according to the structure and sensitivity of the abnormal receptor...
.
In birds, females are the heterogametic sex, as females have one Z and one W chromosome (ZW) and can therefore produce two types of gametes (Z or W oocytes). By contrast, males are ZZ and can produce only one type of gamete (homogametic)—the Z-bearing sperm.
See also
- X chromosome
The 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...
- Y chromosome
The Y chromosome is the sex-determining chromosome in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testis development, thus determining sex. The human Y chromosome is composed of about 60 million base pairs.- Overview :...
, for more information about origins of the XY sex-determination system
- chromosome
A 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...
, for information on abnormalities of the XY sex-determination system
- intersexuality
Intersexuality in humans refers to intermediate or atypical combinations of physical features that usually distinguish male from female. This is usually understood to be congenital, involving chromosome, morphologic, genital and/or gonadal anomalies, such as diversion from stereotypical XX=female...
for information on variations in human sexual forms
- X-inactivation
X-inactivation is a process by which one of the two copies of the X chromosome present in female mammals is inactivated. The inactive X chromosome is silenced by packaging into transcriptionally inactive heterochromatin...
- sexual differentiation
Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote...
, (human)
- testis-determining factor
- Barr body
In those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z, a Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male , rendered inactive in a process called Lyonization...
- Y-chromosomal Adam
In human genetics, Y-chromosomal Adam is the patrilineal human most recent common ancestor from whom all Y chromosomes in living men are descended...
- Sex-determination system
A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. Most sexual organisms have two sexes. In many cases, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual...
- X0 sex-determination system
The X0 sex-determination system is a system that hymenopterans, grasshoppers, crickets, cockroaches, and some other insects use to determine the sex of their offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome , while females have two ....
- ZW sex-determination system
The ZW sex-determination system is a system that determines the sex of offspring in birds, some fish, and some insects , and some reptiles, including Komodo dragons...
- Haplodiploid sex-determination system
External links