X-Ray crystallography of DNA from SLAC
April 2, 2014


Everybody's seen the crime show in which the criminalist swabs somebody's cheek and sticks the Q-tip in a test tube to rush off to the lab. They usually get the results back by the next commercial break, and arrest the perp, usually the one they told that the test is to exclude him from the suspect list. In real life DNA testing takes a lot longer, and the kind of test that you can do from a private company is a bit different.

My wife and I are mildly interested in our genealogy, and we'd thought for a long time that it would be interesting to find out what our DNA said about our ancestors. So we got two of the kits, and sent them back in to 23andMe for testing and evaluation.

The procedure is somewhat different than you see on the crime shows. First off, you don't do a cheek swab. You spit several times into a test tube, and then seal it. I forget whether there's preservative already in the tube, or you add it, or what, but in any case the tube is sealed, and returned to the lab.

Second, in the crime shows it takes a few hours, or at most overnight to get the results back. The results don't comeback from 23andMe for several weeks.

Now when we did we got a report that showed whether we had genetic markers for certain diseases. Unfortunately, the bureaucrats at the outmoded, out of touch FDA put the kibosh on that. We'll get back to that in a moment.

The remainder of the report shows your genetic heritage going back about 500 years. It doesn't specify distant relatives from say the 1700s, but it shows what percentage of your ancestry is traceable to various locations. One of my relatives has traced the genealogy on my mother's side back to the 16ᵗʰ or 17ᵗʰ centuries, and what she's got is Germanic originating in Ljubljana, Slovenia. There was a fairly standard mix of English/Irish, German, and some other groups. Oddly there was .2% Russian element. That works out to 1 in 500, or 9 generations ago. One of the genealogies that my mother had went back about 7 generations and started with a couple having 11 children in the 1850s and 1860s. So 9 generations would put it sometime in the mid-18ᵗʰ century. I've been having fantasies of some guy cuddling up to a Russian cutie on the steppes of Russia. The wind blowing, and the two of them huddled together for warmth in the fierce Russian cold. Of course, I really have no idea what was going on, or who did what to whom.

My wife's ancestry was similar to mine, but she had a bit, roughly the same percentage as mine, of a group that originated in Siberia. Talk about your Russian winters, and huddling up for shared bodily warmth.

The picture at the left shows a sample of the report for elevated risk factors. Note that the results indicate the genetic risk. Other factors, such as diet and exercise, may reduce the risk of contracting some of these diseases. Also bear in mind that the table shows probability, i.e., it is not certain that you'll come down with the disease. I have a .15% chance of developing bipolar disorder, means that while the odds are higher than normal that I'll become bipolar, the odds that I won't mean that it's almost certain that I won't become bipolar. So that's the way to bet.

This figure shows my respons­iveness to drugs.

Now about the idiocrats at the FDA. They put out an order that told 23andMe to stop providing interpretations of the genetic markers to their clients. The ground for this action was that we, the consumers, are too stupid to use the data properly. Now I grant you that there are a lot of stupid people out there, many of them Federal and State idiocrats, but really. Any patient who goes to a doctor with those test results, and says, Doc, I've got the marker for this really bad disease. Can you lop off this organ? and does not get re-tested and re-examined and get a confirmation has got a really bad doctor. It seems to me that since it's my body, my genome, that I have a right to knowledge about my body and my genome, and that it shouldn't be blocked by some bloody minded beureaucrat.

Should you get this kind of genetic testing done? The FDA diminished the value of the test somewhat, but if you're primarily interested in it for the ancestry component, and you want to meet up with some long-lost relatives, go for it.


Ancestry.com stores birth records, and public records such as marriage licenses, military records, death notices, listings from the Social Security Death Index, and records that are input by members of Ancestry. Once you have entered data for your immediate family, you'll probably get some hints, which look like little leaves on the top right of a family member's box. You can follow these hints till they peter out.

Now here's the interesting thing, and I'm afraid that it involves a bit of 8ᵗʰ or 9ᵗʰ grade math. If you start with just yourself, and forget for a minute about your brothers, sisters, half-brothers, half-sisters, you can be represented by a number, that number being 1.

Now any number raised to the power of 0 is 1. So 2⁰ is 1. Any number raised to the power of 1 is itself. So 2¹ is 2. Now your genetic ancestors should appear in powers of 2.

Current Generation
Power of 2
Now if you've been paying attention, you'll have noticed that you plus your parents is one less than your grandparents. So the rule is that adding each term in the series 2⁰..2ⁿ = 2ⁿ⁺¹-1.

This is very similar to a story that is sometimes used to introduce the notion of exponents, the story of the invention of chess. You can find an article about it at Wikipedia as well as here and here This table shows the how the power of 2 grows. The first three or four rows may be familiar, because they are commonly encountered when expressing the size of data in kilobytes, megabytes, gigabytes, and now terabytes.

Power of 2
Logarithmic chart of the power of 2
In the chess problem the answer is 1 less than 2⁶⁴.

When I did our ancestry, I didn't get very far with my side of the family. One branch of my wife's family though kept going and going, and I finally reached Dagobert, the Mild and Loving in 270 or thereabouts. Dagobert is her 59ᵗʰ great-grandfather. So going back to her grandparents and her parents we get 61 generations which means there are 261 great-grandparents of that generation. So she should have over 2 quintillion ancestors in that period. Now that is a conundrum.

The earth didn't reach a population of 1 billion until the last century. There's an old joke about West Virginians, that their family trees don't fork, but I'm afraid that at some point, well not all of our trees fork that sharply. Family lines cross, and in the end, we're all related to each other.

My wife's ancestors include Alaric (sacker of Rome in 410), Clovis (Christianized France), St Clothilde (wife of Clovis), St. Begga, and various knights that in other genealogies are marked as Descendant of Charlemagne. Oddly enough, precisely because the ancestry tree doesn't fork as sharply as it should, most of us are. The phenomenon is discussed here and here.

Unfortunately, my own genealogy can't be traced as far. Some people, for example my paternal grandmother, are rather like Melchizadek in Hebrews 7: Without father or mother, without genealogy, without beginning of days or end of life. My one ancestor of any note is a man who may have been hung. According to family legend as recounted to me some years ago, he was a horse thief.