XCalPab: /* The Onion Test and the C-value Paradox */ typo
The '''Onion Test''' is a way of self-assessing the validity of an argument for a functional role for junk DNA. It was originally proposed<ref name=":02"></ref> informally in a blog post by T Ryan Gregory, a professor at the University of Guelph, Canada, in order to help clarify the debate about [[junk DNA]]. The Onion Test has been frequently cited in newspapers and online media central to the debate<ref>Liquid error: wrong number of arguments (1 for 2)</ref><ref></ref> as well as scientific journal articles<ref>Liquid error: wrong number of arguments (1 for 2)</ref><ref>Liquid error: wrong number of arguments (1 for 2)</ref><ref>Liquid error: wrong number of arguments (1 for 2)</ref><ref>Liquid error: wrong number of arguments (1 for 2)</ref> and textbooks<ref></ref>. The test is defined as:<blockquote>'''The onion test''' is a simple reality check for anyone who thinks they have come up with a universal function for junk DNA. Whatever your proposed function, ask yourself this question: Can I explain why an onion needs about five times more non-coding DNA for this function than a human?</blockquote>Onions and their relatives vary dramatically in their genome sizes,<ref name=":12">Liquid error: wrong number of arguments (1 for 2)</ref> without changing their ploidy, and this gives an exceptionally valuable window on the genomic expansion junk DNA. Since [[onion]] (''Allium cepa'') is a diploid organism having a haploid genome size of 15.9 Gb,<ref name=":12" /> it thus has 4.9x as much DNA as does a [[human genome]] (3.2 Gb). Other species in the genus ''Allium'' vary hugely in DNA content without changing their [[ploidy]]. ''Allium schoenoprasum'' ([[chives]]) for example has a haploid genome size of 7.5 Gb, less than half that of onions, yet [[Allium ursinum]] (wild garlic) has a haploid genome size of 30.9 Gb, nearly twice (1.94x) that of onion and over four times (4.1x) that of chives. This extreme size variation betwen closely related species in the genus Allium is also part of the extended Onion Test rationale as originally defined:<ref name=":02" /><blockquote>Further, if you think perhaps onions are somehow special, consider that members of the genus ''Allium'' range in genome size from 7 pg to 31.5 pg. So why can ''A. altyncolicum'' make do with one fifth as much regulation, structural maintenance, protection against mutagens, or [insert preferred universal function] as ''A. ursinum''?</blockquote>
== The Onion Test and the C-value Paradox ==
The Onion Test is sometimes erroneously confused with the [[C-value|C-value paradox]]<ref name=":22">Liquid error: wrong number of arguments (1 for 2)</ref> particularly among [[Creationism|creationists]]. The onion test however is distinct in that it does not attempt to provide evidence for the existence of junk DNA, but is rather a didactic approach to evaluate any proposed global function for junk-DNA. It asks why allium species need so much more of that proposed function than do humans, and why so much more (or less) than other closely related species of allium.[http://bit.ly/2IbNpcu] It is designed as a method to help interrogate the validity of a proposition, not address the variation in genome size ([[C-value]]) among organisms itself.
== Criticisms of the Onion Test ==
Criticisms of the Onion Test have largely fallen into two camps: Firstly by those conflating the Onion Test and the C-value paradox.<ref name=":22" /> Secondly some explain the difference as a product of [[polyploidy]] and therefore a not relevant to the discussion of humans. Some Allium species are tetraploid, however the species often described in the Onion Test, including onion itself, are diploid like humans. In the original extended Onion Test rationale<ref name=":02" /> Gregory used ''A. altyncolicum'' as an example of an exceptionally small (7pg, 6.9 Gb) Allium genome. This species is most likely tetraploid,<ref name=":12" /> but this perhaps makes the case for highly variable genome size even more strongly, and could be easily replaced with other diploid species such as ''Allium schoenoprasum'' ([[chives]],7.5 Gb).
== References ==
<references />
== The Onion Test and the C-value Paradox ==
The Onion Test is sometimes erroneously confused with the [[C-value|C-value paradox]]<ref name=":22">Liquid error: wrong number of arguments (1 for 2)</ref> particularly among [[Creationism|creationists]]. The onion test however is distinct in that it does not attempt to provide evidence for the existence of junk DNA, but is rather a didactic approach to evaluate any proposed global function for junk-DNA. It asks why allium species need so much more of that proposed function than do humans, and why so much more (or less) than other closely related species of allium.[http://bit.ly/2IbNpcu] It is designed as a method to help interrogate the validity of a proposition, not address the variation in genome size ([[C-value]]) among organisms itself.
== Criticisms of the Onion Test ==
Criticisms of the Onion Test have largely fallen into two camps: Firstly by those conflating the Onion Test and the C-value paradox.<ref name=":22" /> Secondly some explain the difference as a product of [[polyploidy]] and therefore a not relevant to the discussion of humans. Some Allium species are tetraploid, however the species often described in the Onion Test, including onion itself, are diploid like humans. In the original extended Onion Test rationale<ref name=":02" /> Gregory used ''A. altyncolicum'' as an example of an exceptionally small (7pg, 6.9 Gb) Allium genome. This species is most likely tetraploid,<ref name=":12" /> but this perhaps makes the case for highly variable genome size even more strongly, and could be easily replaced with other diploid species such as ''Allium schoenoprasum'' ([[chives]],7.5 Gb).
== References ==
<references />
from Wikipedia - New pages [en] http://bit.ly/2GkKOLq
via IFTTT
No comments:
Post a Comment