Wednesday, September 24, 2008


I really like my public health genetics course. I can't express how much appreciation for life I get from understanding genetics and its implications. Now, I know that for many people their eyes have already glazed over by this sentence, but please bear with me. If you remember nothing else about genetics, remember the number 0.01%. If you want to know why, keep reading.

We are all the same
The human genome is ~3 billion base-pairs large. And that's only one set of chromosomes, really our genome is ~6 billion base-pairs because everyone has a pair of chromosomes (one from dad and one from mom). And that's ~6 billion pairs of the 4 "letters" of the genetic code: A, T, C, and G. Our entire make-up is 4 letters repeated in different combinations.

And the vast majority of our genome is the same amongst each other. In fact, 99.9% of our genome is identical: I have the same As, Ts, Cs, and Gs in exactly the same combination and in exactly the same spot in my genome as the you reading this for 99.9% of my DNA make-up.

An interesting extension of this is that the concept of "race" is artificial. There is more genetic diversity "within a race" than genetic differences "between races." And all the genetic differences between races can be eliminated after a single generation of completely random mating. So while true equality (at least genetically) is impossible for us, if we all have sex at random with any person in the entire world, our children's genomes would largely be free of any differences attributed to race. In other words, the increased incidence of sickle-cell anemia in Africans, cystic fibrosis in Europeans, and lack of alcohol dehydrogenase in Asians (the reason why Asians get drunk so easily), would no longer be coupled with the respective races. It would be distributed more or less evenly amongst everyone.

We are all different
Despite the fact that we all are 99.9% identical, we are also 0.01% different. That doesn't seem like much, but 0.01% of ~3 billion is ~30 million. So what makes me different from you is ~30 million As, Ts, Cs, and Gs. Of these ~30 million differences, about 100 are uniquely mine that will never be seen on the face of the Earth again. And you can bet you have about 100 mutations (simply put, a change in DNA sequence between yours and the person next to you) that is uniquely yours that'll never be seen again either.

And all of our DNA contains relics of our past. With this tiny percentage, with just 0.01%, we can trace back our ancestry for many generations. We are all a mosaic of everyone who has lived before us, we carry within us the DNA that someone had long ago. In a sense, within this 0.01%, we are not really one single person, but rather a collection of thousands that have combined to form a life that's uniquely us.

Also, it's mind-blowing to think that 0.01% of our genome is potentially the cause of so many good and bad things. And all the discrimination, all the hate, all the differences we see in each other, accounts for so little of who we all actually are. If only we could learn to love the other 99.9% . . .

Against genetic determinism
There's this notion that because something is genetic then it's certain. A deterministic view of genetics. There used to be this concept of a "one gene, one disease" model (or OGOD model). In reality, a relatively small proportion of things are strictly determined by genetics alone. Even in embryonic development, the environment in the womb and the mother's diet can have an effect on the outcome of the infant.

And as we age, less and less of what happens to us is a strictly genetic. We may have a gene that predisposes, or increases our risk, of getting a particular disease. But as long as that gene isn't activated or turned on, then it doesn't even really matter. Most of the time it's our external environment - whether we eat healthily, whether we exercise, whether we smoke or not - that acts as the trigger for these genes.

Sometimes, even if a particular gene is activated, it can still be counteracted. Say, even if I have a gene that makes me more likely to be overweight, if I eat right and exercise enough, it won't matter. It just makes it that much harder for me to keep the weight off than it is for someone else, that's all. (Yeah, sounds nice and all but it's still more effort for me.)

In many respects our DNA is indeed a blueprint. But for the rest, it's more of a guideline that we have a fair degree of control over through our own choices and actions.


David said...

my brain hurts. thanks XP

naturgesetz said...

Amazing, innit?

Aek said...

david: You're welcome! But seriously, come on now, that wasn't THAT bad right? XP

naturgesetz: Yeah, I'm always enthralled by genetics when I actually pause to think about it.

steevo said...

GREAT post. I luv that stuff.