Diferenzas entre revisións de «Liña xerminal»

sen resumo de edición
Sem resumo de edição
Sem resumo de edição
 
As [[mutación]]s, recombinacións ou outros cambios xenéticos na liña xerminal poden transmitirse á descendencia, mentres que os cambios nas células somáticas non.<ref>C.Michael Hogan. 2010. [http://www.eoearth.org/article/Mutation?topic=49496 ''Mutation''. ed. E.Monosson and C.J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC]</ref> Isto non se ten que aplicar a organismos que se reproducen somaticamente, como as [[Porifera|esponxas]]<ref name= "Brusca">{{cite book |author1=Brusca, Richard C. |author2=Brusca, Gary J. | title = Invertebrates | publisher = Sinauer Associates | location = Sunderland | year = 1990 | isbn = 0878930981 }}</ref> e moitas plantas. Por exemplo, moitas variedades de ''[[Citrus]]'',<ref>Akira Wakana and Shunpei Uemoto. Adventive Embryogenesis in Citrus (Rutaceae). II. Postfertilization Development. American Journal of Botany Vol. 75, No. 7 (Jul., 1988), pp. 1033-1047 Published by: Botanical Society of America Article Stable URL: http://www.jstor.org/stable/2443771</ref> de [[Rosaceae]] e dalgunhas [[Asteraceae]], como ''[[Taraxacum]]'' producen [[semente]]s por apomixe cando células somáticas [[diploide]]s desprazan o óvulo ou o embrión en fases temperás.<ref name="Peter2009">{{cite book|author=K V Ed Peter|title=Basics Of Horticulture|url=http://books.google.com/books?id=NWMa741kG_gC&pg=PA9|date=5 February 2009|publisher=New India Publishing|isbn=978-81-89422-55-4|pages=9–}}</ref>
 
As [[August Weismann]] proposed and pointed out, a germline cell is immortal in the sense that it is part of a lineage that has reproduced indefinitely since the beginning of life and, barring accident could continue doing so indefinitely.<ref name="Weismann1892">{{cite book|author=August Weismann|title=Essays upon heredity and kindred biological problems|url=http://books.google.com/books?id=dc45AAAAMAAJ|year=1892|publisher=Clarendon press}}</ref> Somatic cells of most organisms however, can only approach any such capability to a limited extent and under special conditions. It is now known in some detail that this distinction between somatic and germ cells is partly artificial and depends on particular circumstances and internal cellular mechanisms such as [[telomeres]] and controls such as the selective application of [[telomerase]] in germ cells, [[stem cells]] and the like.<ref>Watt, F. M. and B. L. M. Hogan. 2000 Out of Eden: Stem Cells and Their Niches ''Science 287:1427-1430''.</ref> Weismann however worked long before such mechanisms were known, let alone [[Epigenetics|epigenetic mechanisms]] or even the genetic role of chromosomes, and he believed that there was some clear qualitative difference between germ cells and somatic cells, though he did realise that the somatic cells [[Cellular differentiation|differentiated]] from the germ cells.<ref name="Weismann1892"/> Many of his views necessarily changed during his life, and some of the resulting inconsistencies were discussed in depth by [[George Romanes]].<ref name="GJR">Romanes, George John. An examination of Weismannism. The Open court publishing company in Chicago 1893 [https://openlibrary.org/books/OL23380098M/An_examination_of_Weismannism]</ref> However Weismann was under no illusions concerning the limitations of his ideas in the absence of hard data concerning the nature of the systems he was speculating on or studying, and he discussed the limitations frankly and analytically.<ref name="Weismann1892"/>
 
O termo ''liña xerminal'' pode utilizarse tamén para indicar a liñaxe de células ao longo de moitas [[xeración]]s de individuos, por exemplo, a liña xerminal que liga calquera individuo co seu hipotético [[último antepasado universal]], do cal descenden todos.
== Notas ==
{{reflist|30em}}
 
== Véxase tamén ==
=== Outros artigos ===
* [[August Weismann]]
* [[Epixenética]]
* [[Barreira de Weismann]]
 
 
 
205.270

edicións