Duck-Billed Treasure Trove

Whose genome matters more–the weirdest mammal or the decoder of DNA? 

This month my mailbox has been filled with genomic goodies. Last month we had Jim Watson’s very own genome–the discoverer of DNA is out there now with all his base pairs.

May 1stNature reported on variation in eight human genomes, not counting Jim’s. The idea was to spot “one-armed bandits,”

sequences that match the standard genome at one end but not the other. These bits not only differ from person to person, but are clues to ongoing evolution.

The New England Journal of Medicine reported that same day on genes for cardiomyopathy. This tragic deterioration of the heart muscle often strikes young people. Most of the familial cases and half the “sporadic” cases in children—those with no known family background–have mutations in the same group of genes. The same issue also reported that a main type of leukemia—(acute myeloid, or AML)— often linked to abnormal chromosomes, is tied to certain genes even if the chromosomes look normal.

The next day, Science had news about the bill restricting misuse of genetic info. Rep. Louise Slaughter (D-NY), a microbiologist, has introduced it thirteen years running, but this year may get lucky. She’s in favor of finding out—“the president of the drug company and the president of the insurance company have bad genes. It’s to their benefit…that we know all we can”—but her bill will help keep them honest about ours.

And on May 6, the New York Times ran a story about a new way to map disease       genes, the “diseaseome.” The map shows ailments as big or small colored circles depending on how many genes are tied to them, and the circles are laid out according to how close the genes are to the next disease over. Muscular dystrophy, it turns out, shares several genes with heart disease.

Francis Collins, one of the top guys in genomics, said, ''I'm shaking my head with disbelief that two genes would pop up in these two diseases that have absolutely nothing in common.” Not yet that is. It may turn out that heart disease drugs help those with MD. Another expert said, future doctors will reclassify diseases based on genes and will chuckle at how we did it back in the early 21st century.

But still the coolest thing was in the May 8th Nature: the genome of the platypus. What a critter. Swimming at a distance it looks like an otter, but close in and you see a big duck-like bill in a furry face and webbed feet sticking out of a furry body. This thing nests like a reptile, pops out eggs like a chicken, and has thick soft fur like a mammal. The hatchling tears its way out of a leathery egg with a special tooth, crawls into mom’s pouch like a newborn kangaroo, and sucks true milk off her belly skin, since she hasn’t evolved nipples. Grown up, it looks more like a pasted-up animal out of a kid’s computer game than a self-respecting product of evolution.

Yet that it is. There are basically two kinds of egg-laying mammals—the other is the spiny anteater–both dwelling down under (in Australia). This now-thin twig of the evolutionary tree used to be all mammals until around 166 million years ago. Not that the platypus hasn’t evolved, but we always figured it was a kind of living fossil.

Now we know that’s true in some ways. It turns out that its genome is about as much of a paste-up as its anatomy and lifestyle. For instance, the genes for making its thumbnail-size eggs are shared with reptiles and birds, but the genes for milk proteins are just like ours.

Other than sheer curiosity, why care? Because this genome is a treasure-chest of information about our own biology. Our genome consists mainly of things we can’t figure out, and so having non-human reference points makes all the difference. Among others, we have genomes for the chimp, rhesus monkey, mouse, chicken, green anole lizard, and puffer fish, with more on the way.

Adding the platypus triangulates us with lizards and chickens and sets us four against our fishy ancestors. Each twig of the tree involved big biological changes, and illuminating them sheds a bright light on us: how our genes work, how our genomes are constructed, how they translate into the proteins that make us unique. There will be secrets here about our reproductive biology, our brains, and our immunity against diseases that we can’t even yet fathom.

And so, of all the genetic discoveries published over the past month, I’m guessing the platypus genome will turn out to be the most important—more anyway than Jim Watson’s, cool as that may be. And oh, it's more evidence that if you don't understand evolution, you will never, ever understand biology.


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