Liña xerminal: Diferenzas entre revisións

Como norma xeral o modo de transmitir o material xenético é un proceso de ''[[reprodución sexual]]''; tipicamente é un proceso que inclúe cambios sistemáticos no material xenético, que se orixinan durante a [[recombinación xenética|recombinación]], [[meiose]] e [[fecundación]] ou [[Fecundación|singamia]] por exemplo. Porén, hai moitas excepcións, como varias formas de [[apomixe]], [[autogamia]], [[partenoxénese#Automixe|automixe]], [[clonación]], ou [[partenoxénese]].<ref name="TarinCano2000">{{cite book|author1=Juan J. Tarin|author2=Antonio Cano|title=Fertilization in Protozoa and Metazoan Animals: Cellular and Molecular Aspects|url=http://books.google.com/books?id=3YguEHvZtjgC|date=14 September 2000|publisher=Springer|isbn=978-3-540-67093-3}}</ref><ref name="LoweHarris2009">{{cite book|author1=Andrew Lowe|author2=Stephen Harris|author3=Paul Ashton|title=Ecological Genetics: Design, Analysis, and Application|url=http://books.google.com/books?id=W3UkvPORFRcC&pg=PA108|date=1 April 2009|publisher=John Wiley & Sons|isbn=978-1-4443-1121-1|pages=108–}}</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"/>