Determinación do sexo ZW: Diferenzas entre revisións
Contido eliminado Contido engadido
Nova páxina: "{{entradución}} A '''determinación do sexo ZW''' é un sistema de determinación do sexo dependente da presenza nas células do individuo dos cromosomas Z e W, de tal modo, que ..." |
Sen resumo de edición |
||
Liña 2:
A '''determinación do sexo ZW''' é un sistema de determinación do sexo dependente da presenza nas células do individuo dos cromosomas Z e W, de tal modo, que os individuos ZZ son machos e os ZW son femias. Este sistema é utilizado principalmente polas [[ave]]s, e tamén se dá nalgúns [[peixe]]s, [[crustáceo]]s como o cangrexo de río xigante ''[[Macrobrachium rosenbergii]]'', algúns [[insecto]]s (fundamentalmente [[bolboreta]]s diúrans e nocturnas) e algúns [[réptil]]es, entre os que está o [[dragón de Komodo]]. O sistema ZW é un sistema cromosómico de determinación do sexo igual ca o XY ou o X0, pero ten bastantes diferenzas con este. No sistema ZW é o [[óvulo]] o que determina o sexo da descendencia (no XY todo depende de se o [[espermatozoide]] leva o [[cromosoma X]] ou o [[cromosoma Y|Y]], e no sistema X0 tamén depende de se o espermatozoide leva X ou non), polo que as denominacións dos cromosomas como Z e W serven para distinguir este sistema do XY. Outra diferenza co sistema XY é que os machos son o sexo homogamético ZZ (con cromosomas sexuais iguais), e as femias son o sexo heterogamético ZW. O cromosoma Z é máis grande e ten máis xenes ca o W.
On November 3, 2010, scientists announced that they discovered a female ''[[Boa constrictor]]'' that can produce offspring without mating and, through such [[asexual reproduction]], produced 22 female offspring that all have a WW chromosome genetic makeup. Although this result has been achieved in laboratory settings previously, never before has it been proven under natural circumstances. It is not clear as to whether the all-female snake babies will eventually mate with a male, or reproduce asexually, or do both as their mother. However, because of their WW chromosomes, any offspring they produce will be female.<ref>{{cite news| url=http://www.cbc.ca/technology/story/2010/11/03/boa-constrictors-virgin-birth.html | work=CBC News | title=Boa constrictor produces fatherless babies | date=November 3, 2010}}</ref>
Liña 8 ⟶ 9:
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.
▲No genes are shared between the avian ZW and mammal XY chromosomes,<ref>{{cite journal |author=Stiglec R, Ezaz T, Graves JA |title=A new look at the evolution of avian sex chromosomes |journal=Cytogenet. Genome Res. |volume=117 |issue=1-4 |pages=103–9 |year=2007 |pmid=17675850 |doi=10.1159/000103170}}</ref> and, from a comparison between chicken and human, the Z chromosome appeared similar to the [[autosomal]] chromosome 9 in human, rather than X or Y, leading researchers to believe the ZW and XY sex determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the [[common ancestor]]. A paper from 2004 compared the chicken Z chromosome with [[platypus]] X chromosomes and suggested that the two systems are related.<ref>{{cite journal | last=Grützner | first=F. | coauthors=Rens, W., Tsend-Ayush, E., El-Mogharbel, N., O'Brien, P.C.M., Jones, R.C., Ferguson-Smith, M.A. and Marshall, J.A. | year=2004 | title=In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes | journal=[[Nature (journal)|Nature]] | volume=432 | pages=913–917 | doi=10.1038/nature03021 | pmid=15502814 | issue=7019}}</ref> The platypus has 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 according to the paper.
==Notas==
| |||