Tag Archives: genetics

This post follows on from my previous post on Sanger sequencing, and is part of an ongoing series that looks at how we take DNA, hidden away in our cell nuclei, into read the sequence of base pairs that make up our genetic code. In this post, we look at the Second Generation Sequencing machines, that are currently sequencing thousands of genomes-worth of DNA per year throughout the world.
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For an embarrassingly long time, I had very little idea how we read people’s DNA. We deal with DNA sequence so often, and use it for such a plethora of things, that if I thought about it at all, my thoughts would have been something along the lines of “er, well, you just, you know, sequence it, right? Run it out on a gel, or, er, something”. I remember years ago admitting this ignorance to a friend, who said “Oh, they have machines that do it”; this response is both reassuring and terrifying. Anyway, I finally rectified my ignorance (about the time I read the book Genomes 3, which filled in a lot of the blanks on the molecular side of my subject); it is actually a pretty fascinating topic, and also a pretty important one, since progress in sequencing technology drives progress in much of genetics generally. So, I thought I’d dedicate a series of posts to sequencing.

While it seems so simple, sequencing DNA is a pretty major challenge. If you ever hold DNA in your hands, it basically takes the form of a long-chained acid dissolved in water. If you want to know something about it you can dye it and run it out on a gel, to see how large the molecules are (large molecules run more slowly through a gel, so you can tell how big the molecule is by how far it moves), but doing much beyond that requires quite a bit of thinking.
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