Friday, January 30

Can your genes tell you who you are?

Article Review: My Genome, My Self - by Steven Pinker

It has now been almost exactly 13 years since the cloning of the first mammal (remember Dolly), and in case you haven’t realized, the genomics revolution is in full swing. For the price of a semester's worth of books, you can have your genome scanned for disease risks, ancestry data, and a small sample of traits; for the price of a luxury car, you can get a “complete” sequence (I use quotations because by complete what is really meant is the 1% that codes for proteins). And unlike most things these days, these prices are dropping precipitously. So the obvious questions are: WHAT CAN OUR GENES TELL US ABOUT WHO WE ARE, and what will be the consequences (good and/or bad) of having that information? Steven Pinker, a Harvard College professor of psychology, recently wrote the cover story for The New York Time Magazine on the topic (to link to the article, click on the title of the post - for some reason a direct link doesn't work, but you should be able to get to it from the page you are directed to).

According to Pinker, the two main concerns that have been raised are:

1) Possible discrimination based on genetic data

2) The possibility of companies taking advantage of hypochondriacs by “turning dubious probabilities into Genes of Doom”

In my opinion, the concerns, while something to be aware of, won’t cause significant problems. Bush has already passed a law against using genetic information as a basis for discrimination in the workplace or for healthcare - and there are many diseases for which tests already exist that can determine your susceptibility, so why should the same info coming from a different source cause a new problem? On top of that, I will explain below how discrimination based on genetic information is (like many forms of discrimination) simply a result of ignorance.

As for advantages, the two most obvious are:

1) The possibility for personalized medicine in which drugs are prescribed according to an individual's unique biochemistry

2) Possibility of being able to focus screening and prevention measures on those with the highest risk

Unfortunately, MOST OF THE POTENTIAL BENEFITS OF PERSONAL GENOME SEQUENCING WON'T BE REALIZED IN OUR LIFETIME. What most people don’t understand (including those who championed in the idea of eugenics, popular with many until relatively recently - Hitler being the most famous) is that there are two basic types of inheritance. The first is called Mendelian (aka qualitative, simple) inheritance.

Mendelian inheritance refers to traits that are the result of a single gene with two different versions. The classic example is from Mendel’s work with peas (hence Mendelian inheritance), in which height is controlled by a single gene with two versions, short and tall. In cases such as this, the trait (height) of an individual can be accurately predicted by which versions of the gene it possesses; tall version = tall plant, small version = small plant (another form of Mendelian inheritance has three classes in which 2 talls = tall, 1 tall + 1 short = medium, and 2 shorts = short). While there are a few examples of human traits that are inherited in this manner (diseases such as eye color, cystic fibrosis, Tay-Sachs; also dwarfism), most follow a much more unpredictable mode of inheritance referred to as non-Mendelian (aka quantitative, complex, polygenic) inheritance.

Non-Mendelian inheritance refers to traits that are a result of many different genes, each contributing only slightly. This is the case for most traits in humans, including intellegence and height. Although we can all appreciate the fact that height is a highly heritable trait - “no one thinks Kareem Abdul-Jabbar just ate more Wheaties growing up than Danny DeVito,” - the reason that there aren’t just two or three classes of people (tall, medium, and short) is because dozens to hundreds of genes control human height, each contributing a small amount. This is the case for probably 99% of human traits.

On top of the fact that most traits are controlled by the small effects of many genes, in both kinds of inheritance, traits are also influenced by two other factors that can’t be predicted by your genome sequence: the environment and random chance. This means that even for Mendelian inheritance, where having a particular form of a gene directly determines the physical form of the trait, there will still be variation. This is inherently clear for anyone who has known identical twins. Their genomes are identical, but their personalities, and even physical appearances, are not. These differences are therefore a result of environment and/or random chance (there are actually many other factors that could cause variation, but I'm probably already getting more technical than I should).

Speaking of random chance, the last point I want to bring up is this: MANY MATHEMATICIANS CONSIDER THE PROBABILITY OF A SINGLE EVENT TO BE A MEANINGLESS CONCEPT. For example, when Pinker had his genome sequenced, he discovered he had a gene conferring upon him an 80% chance of baldness. But he’s not bald and shows no signs of balding being a problem in the future. The problem is trying to apply the proportion of people in a sample to an individual person – as Pinker says, “I’m not 80% bald, or even 80% likely to be bald. The most charitable interpretation of the number when applied to me is, ‘If you knew nothing else about me, your subjective confidence that I am bald, on a scale of 1-10, should be 8'.”

I know this post is a bit more than a nugget, but the overall point is this: don’t expect your genome to tell you much more about yourself than you can already find out by other means. In fact, old school means such as aptitude tests (like IQ scores for intelligence, or time in the fifty meter dash for athletic speed), are still much more accurate and informative - and will continue to be so for quite some time. I don't know about you, but I find some comfort in that. I mean, I think its nice to know that your genome can't tell you who you are, or as someone more poetic than I put it, "YOUR GENES ARE NOT YOUR DESTINY."

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