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Orphan gene

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A. cephalotes: over half of its predicted proteome comprises ORFan genes.

Orphan genes are genes without homologues in genomes of other organisms. In other words, without detectable sequence similarity in the genomes of other organisms.[1] They are defined as genes that lack detectable similarity to genes in other species and therefore no clear signals of common descent can be inferred, forming an enigmatic portion of the genome because their origin and function are mostly unknown.[2] Some authors use the term taxonomically-restricted genes (TRGs) as a more carefull definition taking into consideration the narrow phylogenetic distribution of these genes.[1] They are also called ORFan genes (for "Open Reading Frames of unknown origin").[3] The estimated number of orphans genes vary considerably between species, but 10-30% of all genes in a genome is a commonly cited figure.[2]

Origins

Evolutionists claim that orphan genes evolved from non-coding DNA via random mutational processes as they have no better naturalistic explanation to provide.[4] However, they appear to have no ancestral sequences, but instead have arisen suddenly, fully functional.[5][4] According to Carvunis et al., protein-coding genes can arise either through re-organization of pre-existing genes or de novo.[6] Carvunis acknowledge that de novo gene birth remains poorly understood. Jeffrey Tomkins, on the other hand, states that random mutational events are incapable of producing the complex information encoded in genes.[4] Tomkins exposes that use of the so-called de novo synthesis falls into a circular form of illogical reasoning as follow:

De novo gene synthesis must be true because orphan genes exist and orphan genes exist because of the de novo gene synthesis.[4]

Stephen Meyer points out that orphan genes are found in every major group of organisms including animals and plants as well as both prokaryotic and eukaryotic organisms.[3] In some, such as the A. cephalotes over half of its predicted proteome comprises ORFan genes.[7] Stephen Meyer notes that while some biologists argue that as scientists map the sequence of more genomes, homologues of these orphan genes eventually will be found, but the trend so far is going exactly in the opposite direction.[3]

References

  1. 1.0 1.1 Khalturin, K; Hemmrich, G; Fraune, S; Augustin, R; Bosch, TC (2009). "More than just orphans: are taxonomically-restricted genes important in evolution?". Trends in Genetics 25 (9): 404–413. 
  2. 2.0 2.1 Wissler, L.; Gadau, J.; Simola, D. F.; Helmkampf, M.; Bornberg-Bauer, E. (2013). "Mechanisms and Dynamics of Orphan Gene Emergence in Insect Genomes". Genome Biology and Evolution 5 (2): 439–455. 
  3. 3.0 3.1 3.2 Meyer, Stephen E (2013). Darwin's Doubt: The Explosive Origin of Animal Life and the Case for Intelligent Design. Seattle, WA: Harper One. p. 215-216. ISBN 978-0-06-207147-7. 
  4. 4.0 4.1 4.2 4.3 Tomkins, Jeffrey (2012). More Than a Monkey: The Human-Chimp DNA Similarity Myth. CreateSpace Independent Publishing Platform. p. 31-36. ISBN 978-147525325-2. 
  5. Tautz, D.; Domazet-Lošo, T. (2011). "The evolutionary origin of orphan genes". Nature Reviews Genetics 12: 692–702. PMID 21878963. 
  6. Carvunis, Anne-Ruxandra; Rolland, Thomas; Wapinski, Ilan; Calderwood, Michael A.; Yildirim, Muhammed A.; Simonis, Nicolas; Charloteaux, Benoit; Hidalgo, César A. et al. (24 June 2012). "Proto-genes and de novo gene birth". Nature 487 (7407): 370–374. 
  7. Suen, G.; Teiling, C.; Li, L.; Holt, C.; Abouheif, E.; Bornberg-Bauer, E. , et al. (February 10, 2011). "The Genome Sequence of the Leaf-Cutter Ant Atta cephalotes Reveals Insights into Its Obligate Symbiotic Lifestyle". PLoS Genetics 7 (2). http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002007. 

External links