Friday, November 19, 2010

Underneath a sky of genes

I vividly remember my first DNA prep. I had just started working in Sharon Long’s lab and was being led through the basics, and the DNA prep is one of the most humdrum things done in any microbiology lab. You grow up a few milliliters of bacterial cells in culture broth, concentrate them, and use a combination of chemicals to break them open. They release their DNA and all the other goop that is contained in the cell—so the next step is to get rid of all the other goop. At the last step, you have a clear solution containing the cells’ DNA. You add a bit of ethanol, and magic occurs: the DNA that was dissolved in the solution is no longer soluble. It precipitates, making what looks like a delicate dust-bunny of spider silk floating in a test tube of clear liquid. I had been studying DNA in classes for years, but I’d only seen it in pictures. Here, I started with living things and half an hour later I had a visible tangle of their essence. Nowadays, I teach students how to do this, and even though I spend most of my time thinking biology, I still get a buzz out of this.

We are in the midst of two migrations, here in the central valley. We sit under the “Pacific Flyway,” which routes waterfowl and wading birds from the Alaskan tundra to winter grounds in California and Mexico. I can hear the squeaking of flocks of ducks and the rusty-windmill clatter of sandhill cranes when I walk the dog at night. During the day, I’m mesmerized by these flocks. Hundreds of birds, in long, strung-out, ever-shifting lines, they move into sight from the northern horizon and fade from view in the south. Silhouetted against the overcast sky, they look like strands of spider silk drifting in the wind.

There’s another migration going on right now, a migration we can feel. During my class’s midterm on Wednesday, a normally quiet student sitting in the front row became agitated. She eventually started shaking her hand to remove something, and when I went to look, she was dealing with a teeny spider and a very long length of silk. I gathered up the millimeter-sized spider (and the meter of silk it made) and took it outside. When I looked up at the sky, I could see clots and bunches of spider silk drifting in the breeze, gyrating like dancers in a stately adagio. Some were several meters long, and some were shorter but clumped and clotted. They tumbled and shifted lazily as they rode the wind north. It’s “ballooning” season here in the Central Valley, and millions of baby spiders are dispersing, riding strands of silk wherever the wind will take them.

Shifting and tumbling through the sky, both spider silk and strings of migrating birds visually remind me of that DNA tumbling around in a test tube long ago. But having made biology my study, I feel like I am actually seeing DNA drifting through the skies. Watching spiders drift along like aerial plankton, I am seeing bundles of genes venturing northwards, trusting chance to lead them to new environments. Most of these bundles of genes will perish, meeting fates even worse than exam-taking undergrads, but some will discover a new and friendly place, and these airborne bundles of genes will thrive and produce thousands more spiders. The strings of birds are compelled southwards by their own genes—genes that are using those birds to take them to a place with lots of food, where those genes prepare to reproduce again. The birds’ migratory behavior is written in these genes, edited and revised by millions of years of evolution. As I watch an awkward echelon of sandhill cranes fading in the south above drifts of gossamer, I hope these genes fill our skies for millions of years to come.

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