Everything about The Zw Sex-determination System totally explained
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's 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's 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; ) suggests that the two systems may be related. According to the paper,
platypuses 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.
Further Information
Get more info on 'Zw Sex-determination System'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://zw_sex-determination_system.totallyexplained.com">ZW sex-determination system Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
