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The odds of knowing your cousins: 23andme Part 1

Bizarrely, Jonathan Zittrain turns out to be my cousin — which is odd because I have known him for some time and he is also very active in the online civil rights world. How we came to learn this will be the first of my postings on the future of DNA sequencing and the company 23andMe.

(Follow the genetics for part two and other articles.)

23andMe is one of a small crop of personal genomics companies. For a cash fee (ranging from $400 to $1000, but dropping with regularity) you get a kit to send in a DNA sample. They can’t sequence your genome for that amount today, but they can read around 600,000 “single-nucleotide polymorphisms” (SNPs) which are single-letter locations in the genome that are known to vary among different people, and the subject of various research about disease. 23andMe began hoping to let their customers know about how their own DNA predicted their risk for a variety of different diseases and traits. The result is a collection of information — some of which will just make you worry (or breathe more easily) and some of which is actually useful. However, the company’s second-order goal is the real money-maker. They hope to get the sequenced people to fill out surveys and participate in studies. For example, the more people fill out their weight in surveys, the more likely they might notice, “Hey, all the fat people have this SNP, and the thin people have that SNP, maybe we’ve found something.”

However, recently they added a new feature called “Relative Finder.” With Relative Finder, they will compare your DNA with all the other customers, and see if they can find long identical stretches which are very likely to have come from a common ancestor. The more of this they find, the more closely related two people are. All of us are related, often closer than we think, but this technique, in theory, can identify closer relatives like 1st through 4th cousins. (It gets a bit noisy after this.)

Relative Finder shows you a display listing all the people you are related to in their database, and for some people, it turns out to be a lot. You don’t see the name of the person but you can send them an E-mail, and if they agree and respond, you can talk, or even compare your genomes to see where you have matching DNA.

For me it showed one third cousin, and about a dozen 4th cousins. Many people don’t get many relatives that close. A third cousin, if you were wondering, is somebody who shares a great-great-grandparent with you, or more typically a pair of them. It means that your grandparents and their grandparents were “1st” cousins (ordinary cousins.) Most people don’t have much contact with 3rd cousins or care much to. It’s not a very close relationship.

However, I was greatly shocked to see the response that this mystery cousin was Jonathan Zittrain. Jonathan and I are not close friends, more appropriately we might be called friendly colleagues in the cyberlaw field, he being a founder of the Berkman Center and I being at the EFF. But we had seen one another a few times in the prior month, and both lectured recently at the new Singularity University, so we are not distant acquaintances either. Still, it was rather shocking to see this result. I was curious to try to figure out what the odds of it are.  read more »