Friday, December 09, 2005

Tasha's DNA

The big biology news of the past week was the release of the draft sequence of the genome of a boxer named Tasha. This particular dog was selected because she was especially inbred, which should simplify the mapping of behavioral traits and genetic diseases.

This study is important, in part, because inbred dog breeds show very specific behaviors - think herding in sheep dogs, for example - and study of dog genomes can help understand their genetic basis. The sequence can also help us understand human genetics:
The study authors have "pretty much unlocked a treasure chest of genetic variability that underlies phenotypic variability, that helps us to understand not only what regulates traits in dogs but also what regulates traits in humans," canine geneticist Patrick Venta of Michigan State University, who was not involved in the study, told The Scientist. "There's no other mammalian species that has as much genetic variability that causes so much phenotypic variability."
One slightly puzzling aspect of the news, as reported, is that only 5% of the human genome appears to be the same as the dog genome, a figure that sounds much too low. The apparent paradox is explained by RPM of the evolgen blog: much of the conservation lies outside the protein coding regions of DNA (which comprise only 1-2% of the genome). This means that many of the conserved DNA sequences are probably elements that control the expression of the protein coding genes. As noted by one of the authors:
The very most conserved sections that we found reside in the proximity of developmental genes, suggesting that we have found new regulatory elements in the human genome," said co-author Kerstin Lindblad-Toh of the Broad Institute at the Massachusetts Institute of Technology.
This means that the comparison of new dog genomic sequence to the human and mouse genomic sequences has the potential to vastly improve the understanding of how essentially the same set of protein coding genes can be used to build very different animals (from mice to dogs to humans). You can read more about not so junky "junk DNA" at The Loom.

Even better: watch the 2005 HHMI Holiday Lectures by Sean Carroll and David Kingsley on "Evolution: Constant Change and Common Threads", particularly Lecture 4: From Butterflies to Humans.

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