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  Topic: Possom Genome, The Sequencing of Monodelphis domestica< Next Oldest | Next Newest >  
Lou FCD



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Joined: Jan. 2006

(Permalink) Posted: May 25 2007,04:10   

Full Text @ Nature

The abstract:

Quote
We report a high-quality draft of the genome sequence of the grey, short-tailed opossum (Monodelphis domestica). As the first metatherian ('marsupial') species to be sequenced, the opossum provides a unique perspective on the organization and evolution of mammalian genomes. Distinctive features of the opossum chromosomes provide support for recent theories about genome evolution and function, including a strong influence of biased gene conversion on nucleotide sequence composition, and a relationship between chromosomal characteristics and X chromosome inactivation. Comparison of opossum and eutherian genomes also reveals a sharp difference in evolutionary innovation between protein-coding and non-coding functional elements. True innovation in protein-coding genes seems to be relatively rare, with lineage-specific differences being largely due to diversification and rapid turnover in gene families involved in environmental interactions. In contrast, about 20% of eutherian conserved non-coding elements (CNEs) are recent inventions that postdate the divergence of Eutheria and Metatheria. A substantial proportion of these eutherian-specific CNEs arose from sequence inserted by transposable elements, pointing to transposons as a major creative force in the evolution of mammalian gene regulation.




In English @ Science

Quote
By Elizabeth Pennisi
ScienceNOW Daily News
9 May 2007
It may lack the charisma of a koala or a kangaroo, but the gray short-haired opossum has now earned its place in history as the first marsupial to have its DNA deciphered. One of a few creatures that gives birth to highly immature young that then are nourished--often in pouches--outside the womb, the opossum stands in sharp contrast to the other mammals--such as human, mouse, chimpanzee, and macaque--with sequenced genomes. Although its 3.4 billion bases reveal some differences with placental mammals, the opossum's immune system is surprisingly sophisticated, an international team reports today.

Unraveling the genomes of dozens of animals with varying degrees of relatedness is key to learning how humans evolved. Researchers decided to sequence this opossum, Monodelphis domestica, in part because marsupials branched off the mammalian evolutionary tree 180 million years ago. In addition, this species is used in immunology, developmental biology, and biomedical research.

The marsupial's genome holds some surprises. Reporting today in Nature, a team led by Tarjei Mikkelsen and Kerstin Lindblad-Toh of the Broad Institute of the Massachusetts Institute of Technology and Harvard in Cambridge, Massachusetts, shows that of the marsupial's 19,000 or so genes, more than 15,000 clearly correspond to human genes, including an unexpected number important to the body's defenses. That's intriguing, the researchers say, because the marsupial immune system is supposed to be primitive.


The Science article was rather good and worth reading in full.  Lots of good material in there for gratuitous cheap shots at Behe's Folly.

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Henry J



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Joined: Mar. 2005

(Permalink) Posted: May 25 2007,11:56   

Re "That's intriguing, the researchers say, because the marsupial immune system is supposed to be primitive."

Wonder if anybody had a good reason for supposing that in the first place?

Henry

  
Ichthyic



Posts: 3325
Joined: May 2006

(Permalink) Posted: May 25 2007,16:54   

all current phylogenies put marsupials as branching off earlier than placental mammals.

I think this is the main thing here that is meant here by the term "primitive".

example:

http://www.tolweb.org/Mammalia

also, I would wager (without knowing for sure) that marsupial immune systems differ in certain ways that would include fewer components.

Weren't marsupial immune systems actually used to rebut Behe's argument at some point?  I have a foggy memory of something along these lines.

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"And the sea will grant each man new hope..."

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Ichthyic



Posts: 3325
Joined: May 2006

(Permalink) Posted: May 25 2007,16:56   

duplicate, ignore

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"And the sea will grant each man new hope..."

-CC

  
qetzal



Posts: 311
Joined: Feb. 2006

(Permalink) Posted: May 25 2007,21:36   

Quote (Ichthyic @ May 25 2007,16:54)
all current phylogenies put marsupials as branching off earlier than placental mammals.

I think this is the main thing here that is meant here by the term "primitive".

example:

http://www.tolweb.org/Mammalia

also, I would wager (without knowing for sure) that marsupial immune systems differ in certain ways that would include fewer components.

Here's one account of why marsupial immune systems have been considered primitive (source):

 
Quote
[U]nsuccessful attempts to isolate T cell derived cytokines in the laboratory has led some authors to suggest that the marsupial immune system is 'primitive' and does not possess the level of complexity demonstrated by eutherians such as humans and mice. The fact that some T cell driven responses are also aberrant adds to this argument. Marsupials appear to have delayed skin graft rejection [18] and antibody class switching [19], together with an apparent lack of an in vitro Mixed Lymphocyte Response [20].


Also, I don't see how the branching of marsupials from placental mammals says anything about which is more 'primitive.' They branched from one another, so both groups go back to to the same point in time. The only way marsupials can be considered more primitive than eutherians is if they retain more characters of the last common ancestor.

At least, that's my understanding.

  
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