“Mysteries of DNA” image courtesy Mark H. Adams. Full-size version.

As anyone who follows this blog knows, I recently took a 23andMe genetic test and have been blogging about it ever since. Today I thought I would focus on one of the fun parts of the service: traits.

Lots of our traits are at least partly dependent on our genes. So a genetic test should be able to tell me a bit about what I’ll look and even be like in the future. It may even tell me what I can expect for my kids.

Here is what is available on the 23andMe test (click on the image for a larger version):


As you can see, some of this is pretty obvious…I know my eye color for example. It is kind of cool to see my blue eyes written in my DNA but not necessarily that helpful. When I click on eye color, I find out that people with this particular bit of DNA have a 72% chance for blue eyes, a 27% chance for green and a 1% for brown. (Incidentally, this 1% brown is probably a big reason why blue-eyed parents can have a brown-eyed child.)

What would have made this report more interesting for me is what it meant for my kids’ eye color. Does it mean I’ll have blue-eyed kids? This of course depends on my wife’s genes but it would be cool to have the option of including my wife’s data to find out.

Other less obvious traits were very interesting to me. The results say that like most mammals, I should be lactose intolerant. Which I am not—I’m fine drinking milk. So did 23andMe get it wrong?

Probably not. The science is pretty good on this topic. People with a certain difference in their lactase gene almost always lose the ability to make lactase as adults. No lactase means lactose intolerance.

When I dug deeper on the website I got some hand waving about other genetic influences or the environment. A better explanation is that I will probably become lactose intolerant at some point in my adult life—it just hasn’t happened yet.

Losing the ability to make lactase is a gradual thing. It happens to some people early in adulthood and others later on. I am probably one of the “later ons.” Something to look forward to…

One trait that I’ve always been a bit interested in is HIV resistance. Some people are more resistant to infection by HIV (the virus that causes AIDS). If these people do become infected, they tend to develop AIDS symptoms much more slowly as well.

In Europeans at least, this resistance has been tied to a DNA difference called CCR5-delta32. The people who are resistant to infection and who develop AIDS more gradually tend to have two copies of this DNA difference.

This DNA difference has been proposed to have become common in Europeans because it also makes people resistant to either the plague or smallpox. If true, my ancestors must have died like flies from the plague or smallpox because I don’t have the DNA difference.

I also now know about what my DNA tells me about my earwax, how I respond to a certain bitter chemical, and whether I flush from alcohol. These are sort of interesting but not very.

This part of the 23andMe experience is kind of fun though. I really enjoy it when genetic theory matches up with what I can see about me. It sort of validates genetics…

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Trick or Trait 2 October,2015Dr. Barry Starr

  • Ponto

    You lack the lactase retention SNP use by 23andMe which applies to Europeans. I don’t have it either. Like you, I am not intolerant, I am fine with milk. The two of us now just go through 2 to 3 litres of milk per week. My partner uses as much milk as I and neither of us use milk as a drink on its own. I prefer flavored milk as a drink, coffee flavored. Once an adult there are a lot of disadvantages to drinking milk. The main one is the fat content, no skinny milk in my household. Milk also carries a high calorific load.

    As Africans and other milk consuming peoples show, there are other SNPs or genes which enable the production of lactase in adults. Could be you and I have SNPs not scanned by 23andMe which confer lactose tolerance.

    I found 23andMe’s results fairly accurate but on some things they missed out. For instance I have the baldness SNP, actually more than one, but I am not bald. I am 57 years old. I also don’t have asthma or a cleft palette despite what my SNPs suggest. Obviously those SNPs vary in their effects from nil to severe. That is what 23andMe don’t factor in their results.

  • Thanks for the comment. I should have mentioned that the results depend on where a person’s ancestors came from. Might be useful if 23andMe had a way to link ancestry and traits to give a better answer for the person.

    My continued lactose tolerance is probably not due to a different ethnic background…I am definitely Caucasian. But I could have a different SNP, the original scan didn’t look at every European’s DNA!

    In fact 23andMe and companies like them might be a great way to find new SNPs associated with lactose tolerance. Assuming they survive, they will eventually have access to way more DNA than most researchers. If only they can get accurate information about their customers’ traits from their customers.

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Dr. Barry Starr

Dr. Barry Starr (@geneticsboy) is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA and runs their Stanford at The Tech program. The program is part of an ongoing collaboration between the Stanford Department of Genetics and The Tech Museum of Innovation. Together these two partners created the Genetics: Technology with a Twist exhibition.

You can also see additional posts by Barry at KQED Science, and read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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