>I would love to know that reference. But isn't is possible that this gene never became a pseudogene in the first place?
Possible, but rather unlikely. My source is Graur and Li, 2000, Fundamentals of Molecular Evolution, Sinauer Associates, Sunderland, Mass., p. 315-317; their key source seems to be Trabesinger-Ruef et al. 1996. Pseudogenes in ribonuclease evolution: a new source of biomacromolecular function. FEBS Letters 382:319-322.
Pancreatic ribonuclease is single-copy in most mammals. Somewhere in the base of the ruminant clade, it was duplicated twice. One of these duplicate copies is a pseudogene in deer, giraffes, sheep, antelopes, kudu, etc. but functional in Cape buffalo, water buffalo, and cattle as seminal ribonuclease. A relatively small portion of the end of the gene in these bovids now matches the pancreatic ribonuclease gene, correcting a frameshift and restoring two key amino acids. Assuming that the gene actually remained functional in the cattle lineage would require at least four independent conversions to a pseudogene and would not account for the greater similarity between the one region of the new gene and the ancestral gene.
>It seems to me that the possibility of pseudogenes generating variability is very small. I think that a more reasonable alternative would be that duplicated gene are co-opted to other functions without ever becoming pseudogenes. If this is true, the existence of pseudogenes could be just a byproduct of the generation of variation through gene duplication. Does this make sense?
Yes, that seems much more likely. Occasionally, a pseudogene may become functional, but probably only rarely. Graur and Li also note a case (in horses) where a pseudogene has remained almost identical to the functional gene. A pseudogene in this situation could be readily revived.
Dr. David Campbell
"Old Seashells"
Biology Department
Saint Mary's College of Maryland
18952 E. Fisher Road
St. Mary's City, MD 20686-3001 USA
dcampbell@osprey.smcm.edu, 301 862-0372 Fax: 301 862-0996
"Mollusks murmured 'Morning!'. And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!
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