cryptoguru
Posts: 53
Joined: Jan. 2015
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| Quote | Regarding ORFan genes:
What percentage of genomes have been sequenced and cataloged?
Does having no cousins logically prove that one has no parents? |
midwifetoad: excellent question ... they assumed this was the case when they first started finding them. The theory went, that the ratio of ORFan genes to those which are represented in other organisms would start to level off as we sequence more genomes. Fact is they are linear and continue to grow linearly the more we sequence.
We obviously know an organism has parents, but this evidence pushes against the assumption of cousins in other species. You can't claim we're 96% chimp and at the same time say that 20-40% of our DNA is not found anywhere else. If you are assuming common ancestry between 2 species you need to be able to explain the divergence of their DNA. Previously we categorised the non-coding DNA as junk, now we know it isn't junk ... so we have to account for the information in the non-coding DNA now too which contains many ORFan genes (i.e. we're not 96% chimp). If we have to account for a minimum of 20% of our DNA being de novo in the last 13 Million years, we have to believe in minimum 500 advantageous mutations preserved every single generation. That is provably false.
http://mic.sgmjournals.org/content....99.full
quote from this article
| Quote | | Fig. 1(a)⇓ shows that the number of these orphan bacterial genes is continuing to rise in a roughly linear fashion despite the large number of genomes sequenced, and this trend shows no signs of levelling off. In fact, the last 30 species included in this study provided 30 % of the total orphans in our study (mean=441±643 for dataset D1; despite the large standard deviation all species contributed orphans). |
and from this New Scientist article
http://ccsb.dfci.harvard.edu/web....013.pdf
| Quote | Some other researchers, however, are
starting to think it may be surprisingly
common. A study of 270primate orphan
genes, led by M. Mar Albà and Macarena
Toll-Riera of the Municipal Foundation
Institute for Medical Research in Barcelona,
Spain, found that only a quarter could be
explained by rapid evolution after duplication
(Molecular Biology and Evolution, vol 26, p
603). Instead, around 60 per cent appeared
to be new. |
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