Moontanman Posted August 8, 2012 Posted August 8, 2012 Paddlefish's Doubled Genome May Question Theories On Limb Evolution ScienceDaily (Aug. 6, 2012) — The American paddlefish -- known for its bizarre, protruding snout and eggs harvested for caviar -- duplicated its entire genome about 42 million years ago, according to a new study published in the journal Genome Biology and Evolution. This finding may add a new twist to the way scientists study how fins evolved into limbs since the paddlefish is often used as a proxy for a more representative ancestor shared by humans and fishes. A juvenile paddlefish, just under three inches long at two months old. Fully grown American paddlefish can reach five feet (1.5 m) in length and have a protruding snout or "rostrum." A new study by researchers at San Francisco State University finds that the American paddlefish underwent a genome duplication 42 million years ago. (Credit: Diane Fenster/ San Francisco State University)
jimmydasaint Posted August 8, 2012 Posted August 8, 2012 Interesting find Moontanman, I think the researchers looked at the every interesting Hox (or homeotic box) genes. IIRC, these genes are like a molecular 'flag' which are pointers for body parts to be made by the protein generating machinery of the cell. For example, some Hox genes may be responsible for organising head development and others for development of the thorax. I think the researchers found that the whole genome duplication allowed two sets of genes to be present simultaneousy in the organism for limbs etc... One set would be conserved whilst the other would act as a substrate for evolution events and could result in a new type of limb or body structure which would then be open to selection (or extinction) by the environment. Crow and colleagues sequenced chromosomal regions containing 19 Hox genes in the American paddlefish. Hox genes determine body shape and limb development, and have become prime candidates for detecting whole genome duplications. Whole genome duplications are game-changing events in evolutionary history that give rise to new species or novel features within a species. They occur when a series of unlikely circumstances coincide, resulting in twin copies of every gene. When this happens, one scenario that could take place is that one gene in the pair keeps its designated function while the other is either lost or takes on a new purpose. "This extra genetic material provides the canvas for evolution to paint with," said Crow, who studies the evolution of novelty and diversity. Two milestone genome duplications are believed to have taken place before the evolution of jawed vertebrates. Additional whole genome duplications have also taken place further down the evolutionary tree, in specific lineages or branches, but it is a phenomenon more common in plants than animals. "Our findings on the paddlefish suggest that whole duplication is not as uncommon in animals as previously thought," Crow said. ScienceDaily article
Moontanman Posted August 8, 2012 Author Posted August 8, 2012 I have an interest in paddlefish to start with, they are a hold over from a time when the dominant animals were literally quite different from what we see today. I have it on pretty good authority that paddlefish breeding has been part of an effort to bred a paddlefish that lacks the paddle feature. Since captive paddlefish being raised for eggs or meat do not need the paddle breeding a paddle less paddlefish could allow for better growth since it would mean more paddlefish and less paddle, the paddle does take up a lot of energy to grow and makes it more difficult to keep the paddlefish in enclosed areas. It was found that the paddle is highly conserved and efforts to eliminate have been unsuccessful... I'm not sure but my money is on the HOX genes being responsible for the paddle in some way and removing the paddle would result in removing genes that are important for other reasons. Paddlefish are very interesting fishes, an ancient linage, that predates dinosaurs, quite possibly even bony fishes, the now considered extinct Chinese paddlefish is, or was, a predator, very much shark like in many ways and yet totally unlike the shark in many others, To me it's a glimpse into what fishes were like before bony fishes evolved or at least became dominant...
akh Posted August 9, 2012 Posted August 9, 2012 It was found that the paddle is highly conserved and efforts to eliminate have been unsuccessful... I'm not sure but my money is on the HOX genes being responsible for the paddle in some way and removing the paddle would result in removing genes that are important for other reasons. I think this is a valid assumption.
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