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ZW sex-determination system

 

 
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ZW sex-determination system
 
 
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The ZW sex-determination system is a system that determines the sex of offspring in birds, some fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
, and some insects (including butterflies and moths
Moths

Moths may refer to:* Gustav Moths , German rower* Moths , Lower Definition's first full-length album* The Moths!, an English indie rock band...
). In the ZW system it is the 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....
 that determines the sex of the offspring, in contrast to the XY sex-determination system
XY sex-determination system

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex....
 and the X0 sex-determination system
X0 sex-determination system

The X0 sex-determination system is a system that hymenoptera, grasshoppers, crickets, cockroaches, and some other insects use to determine the sex of their offspring....
, where it is the sperm
Sperm

The term sperm is derived from the Greek word sperma and refers to the male reproductive Cell . 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....
 which determines the sex. The letters Z and W are used to distinguish this system from the XY system. Males are the homogametic sex
Homogametic sex

Homogametic sex refers to the sex of a species in which both sex chromosomes are identical. For example, in humans, females having two X sex chromosomes would be referred to as the homogametic sex while males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex....
 (ZZ), while females are heterogametic (ZW).






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The ZW sex-determination system is a system that determines the sex of offspring in birds, some fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
, and some insects (including butterflies and moths
Moths

Moths may refer to:* Gustav Moths , German rower* Moths , Lower Definition's first full-length album* The Moths!, an English indie rock band...
). In the ZW system it is the 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....
 that determines the sex of the offspring, in contrast to the XY sex-determination system
XY sex-determination system

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex....
 and the X0 sex-determination system
X0 sex-determination system

The X0 sex-determination system is a system that hymenoptera, grasshoppers, crickets, cockroaches, and some other insects use to determine the sex of their offspring....
, where it is the sperm
Sperm

The term sperm is derived from the Greek word sperma and refers to the male reproductive Cell . 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....
 which determines the sex. The letters Z and W are used to distinguish this system from the XY system. Males are the homogametic sex
Homogametic sex

Homogametic sex refers to the sex of a species in which both sex chromosomes are identical. For example, in humans, females having two X sex chromosomes would be referred to as the homogametic sex while males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex....
 (ZZ), while females are heterogametic (ZW). The Z chromosome is larger and has more genes, like the X chromosome in the XY system.

It is unknown whether the presence of the W chromosome induces female features or the duplication of the Z chromosome induces male ones; unlike mammals, no birds with a double W chromosome (ZWW) or a single Z (Z0) have been discovered. It is possible that either condition causes embryonic death, and both chromosomes are responsible for gender selection; or it may just be that ZWW is just as rare in birds as Turner's syndrome (X0) or Klinefelter's syndrome
Klinefelter's syndrome

Klinefelter's syndrome, 47,XXY or XXY syndrome is a condition in which males have an extra X sex chromosome.While females have an XX chromosomal makeup, and males an XY, Affected individuals have at least two X chromosomes and at least one Y chromosome....
 (XXY) are in humans, and without having any reason to check individual animals for this, it has never been found.

In Lepidoptera
Lepidoptera

Lepidoptera is an order of insect that includes moths and butterfly. It is one of the most speciose orders in the class Insecta, encompassing moths and the three superfamilies of butterfly, skipper , and Hedylidae....
 (moths and butterflies), examples of Z0, ZZW and ZZWW females can be found. This suggests that the W chromosome is essential in female determination in some species (ZZW), but not in others (Z0). In Bombyx mori
Bombyx mori

The silkworm is the larva or caterpillar of Bombyx mori , the domesticated silkmoth. A moth in the family Bombycidae, it is very important economically as the producer of silk....
 (the commercial silkworm), the W chromosome carries the female-determining genes.

Chromosomes in the ZW region in birds are autosomal in mammals, and vice-versa; therefore, it is theorized that the ZW and XY couples come from different chromosomes of the common ancestor. A paper published in 2004 suggests that the two systems may be related. According to the paper, platypodes
Platypus

The Platypus is a semi-aquatic mammal Endemic to Eastern states of Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay Egg instead of giving birth to live young....
 have a ten-chromosome
Chromosome

A chromosome is an organized structure of DNA and protein that is found in Cell . A chromosome is a single piece of DNA that contains many genes, regulatory sequence and other genetic sequence....
–based system, where the chromosomes form a multivalent chain in male meiosis
Meiosis

In biology or life science, meiosis is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores....
, segregating into XXXXX-sperm and YYYYY-sperm, with XY-equivalent chromosomes at one end of this chain and the ZW-equivalent chromosomes at the other end.

See also

  • Chromosome
    Chromosome

    A chromosome is an organized structure of DNA and protein that is found in Cell . A chromosome is a single piece of DNA that contains many genes, regulatory sequence and other genetic sequence....
  • Haplodiploid sex-determination system
  • Sex-determination system
    Sex-determination system

    A sex-determination system is a biology system that determines the development of sex 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 Comparative anatomy....
  • Sexual differentiation
    Sexual differentiation

    Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote . As male and female individuals develop from zygotes into fetuses, into infants, children, adolescents, and eventually into adults, sex and gender differences at many levels develop: genes, chromosomes, gonads, ho...
  • X chromosome
    X chromosome

    The X chromosome is one of the two sex determination system chromosomes in many animal species, including mammals . It is a part of the XY sex-determination system and X0 sex-determination system....
  • XY sex-determination system
    XY sex-determination system

    The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects and some plants . In this system, females have two of the same kind of sex chromosome , and are called the homogametic sex....
  • X0 sex-determination system
    X0 sex-determination system

    The X0 sex-determination system is a system that hymenoptera, grasshoppers, crickets, cockroaches, and some other insects use to determine the sex of their offspring....
  • Y chromosome
    Y chromosome

    The Y chromosome is the Sex-determination system chromosome in most mammals, including humans. In mammals, it contains the gene SRY, which triggers testicle development, thus determining sex....