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 some insects (including butterflies and moths). In the ZW system it is the ovum that determines the sex of the offspring, in contrast to the XY sex-determination system and the X0 sex-determination system. The letters Z and W are used to distinguish this system from XY system. Males are the homogametic 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 (XO) or Klinefelter's syndrome (XXY) is in humans, and without having any reason to check individual animals for this, it has never been found.

In Lepidoptera (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" (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 (Frank Grützner "et al", "Nature"; doi|10.1038/nature03021) suggests that the two systems may be related. According to the paper, platypodes have a ten-chromosome–based system, where the chromosomes form a multivalent chain in male meiosis, 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

*X chromosome
*Y chromosome
*chromosome
*sexual differentiation
*Sex-determination system
**XY sex-determination system
**X0 sex-determination system
**Haplodiploid sex-determination system


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • 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… …   Wikipedia

  • XY sex-determination system — Drosophila sex chromosomes The XY sex determination system is the sex determination system found in humans, most other mammals, some insects (Drosophila) and some plants (Ginkgo). In this system, females have two of the same kind of sex… …   Wikipedia

  • Haplodiploid sex-determination system — The haplodiploid sex determination system determines the sex of the offspring of many Hymenopterans (bees, ants, and wasps), and coleopterans (bark beetles). In this system, sex is determined by the number of sets of chromosomes an individual… …   Wikipedia

  • X0 sex-determination system — The X0 sex determination system is a system that 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… …   Wikipedia

  • Temperature-dependent sex determination — (TSD), also called environmental sex determination [http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature06519.html The adaptive significance of temperature dependent sex determination in a reptile] from Nature ] , is where the… …   Wikipedia

  • Maternal influence on sex determination — In humans and several other species of animals, the father determines the sex of the child. In the XY sex determination system, the female provided ovum contributes an X chromosome and the male provided sperm contributes either an X chromosome or …   Wikipedia

  • Sex ratio — is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms. [Nancy S. Coney and W. C.… …   Wikipedia

  • Complementary Sex Determination — Mit Komplementäre Geschlechtsbestimmung (engl. complementary sex determination) wird ein System der Geschlechtsdetermination bei einigen hymenopteren Arten (Hautflüglern) bezeichnet. Bei normaler Haplodiploidie bei Hautflüglern (Hymenoptera) wird …   Deutsch Wikipedia

  • Sex — An organism s sex is defined by the gametes it produces: males produce male gametes (spermatozoa, or sperm) while females produce female gametes (ova, or egg cells); individual organisms which produce both male and female gametes are termed… …   Wikipedia

  • Sex allocation — is the allocation of resources to male versus female reproduction in sexual species (Charnov 1982). Sex allocation depends upon the breeding system of a species, as well as how reproduction is carried out within each breeding system. Breeding… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”