Monday, August 29, 2005

It's DNA'd confusing...

I've been reading "The Genomics Age: How DNA Technology is Transforming the Way We Live and Who We Are", by Gina Smith. It's a rather grandiose title for the contents, really. It's science for the masses, and as a result, I'm sure there is some tremendous over-simplification going on. That's okay. If it weren't really simple, I'd be too lost to enjoy it. But as a result of the simplification, I'm awash in questions provoked by the text, to which the text does not provide answers. Poop. Any geneticists out there who care to try to reduce their subject to kindergarten level for me, just for two questions?? Question 1: "There turns out to be no such thing as race at the DNA level...In other words, you cannot tell simply by looking at someone's DNA whether they are black or white. Genotype (the description of a person's DNA) should not be confused with phenotype (what they actually look like)." P. 58-59 All right. I knew that there is only one "Human Race". This is not news to me. I can also see that phenotype doesn't mesh exactly with genotype, because even clones (identical twins) have differences. Though their DNA is identical, you can, if you know them well, tell them apart. But, come on now, the differences are subtle! We do get hair colour, height, shape of nose, etc, from our genes. If ethnic differences don't show up in our genes and chromosomes, then why do we, unless intermarriage occurs, breed true to type? Why don't the occasional white couple produce - surprise! - a baby with "oriental" eyes, or an oriental couple produce a child with super-curly afro hair? Question 2: Mitochrondrial DNA. This stuff has me flummoxed and intrigued in equal measure. Mitochrondrial DNA is not found in the nucleus of the cell with the other DNA, but outside, in the rest of the cell. "Because [it] doesn't recombine with the father's's DNA every time a couple has children, it stays pure. That means the mitochrondrial DNA you have in your cells is exactly the same as the mitochondria in your mother's cells, your mother's mother's cells, and so on. It is a perfect line of descent. That makes it theoretically possible to trace back the DNA in all our mitochondria to a handful or original females." p. 86 An argument for Eve! How cool! Okay. So if it stays pure down the matrilineal line, do men have it? And if it's outside the nucleus and doesn't recombine with the father's contribution, how does it get passed on? I'm baffled. And if there are no geneticists reading this, it's back to the books and the googling for me. This is interesting stuff!


Blogger Aginoth said...

I tried taking my Genes back for a refund but was refused even though they are faulty

8/29/2005 03:10:00 PM  
Blogger Heather said...

Those are great questions Mary! I know a *little* about race - from a course in Physical Anthropology in my youth. Race is a theory, in all respects. There is no one gene for race - but lots of genes for the characteristics of "racial characteristics" - - thats over similifying a little. I probably do not have the genes to produce a child with straight, black hair, honey colored skin, epicanthic eye folds (what makes Asians look almond shaped and "asian") - all those traits are parts of many genes. The more you reproduce with people with them the more likely those genes will be expressed. That is why Children of "mixed" descent - say Asian and Caucasian have bits of both - keeping in mind that dominant genes such as brown eyes will be expressed unless parents with recessive blue eyed genes meet. I probably don't have that genetic make-up to produce a remotely asian child with someone of like descendence. Many of the racial characteristics developed over long periods of time in response to climate. What researchers are not sure of is if Homo Sapiens migrated from Africa and into Asia and Europe and elsewhere - or if Homo Erectus migrated and settled throughtout the world and there was parallel evolution to Homo Sapiens in different areas of the world. Anyway. That was a tangent.

Second question. Eric and I were discussing this, and Eric's hypothesis is one that makes sense, but is a wild guess. His is that the genetic code to to enable a being to produce Mitochondrial DNA is only found on the mothers contribution. (Remember chromosomes in an egg or a sperm are not paired). He thinks that mDNA info might not be on the male half of the contribution.

Wild guess.

Great questions!


8/29/2005 05:39:00 PM  
Blogger evilsciencechick said...

OK, Z sent me over here to help you. I am a graduate student studying...genetics. I think I can help you.

1. It's true that there is no overall "racial" genome. Our genes are not identical, but anyone "looking" at both our genomes would not be able to tell our races - our genomes are organized the same way and have the same number of chromosomes (in a normal healthy person, at least). But when you talk about eye shape and hair type, you are talking about specific characteristics. There are genes that determine eye shape, yes. Multiple genes (though I'm assuming that). But even asian eyes are not all identical. Tiny differences between those genes give hundreds if not thousands of variations in eye shape, size, and color. So there is not one "standard" set for "asian eyes." Rather, it is is multitude of tiny differences that make an asian person's eyes different from mine. HOWEVER, the genes that determine shape are mostly the same - it's the same gene, in the same place, that holds the blueprint for only a VERY slightly different protein.

As for why anglo people don't have kids with asian eyes - well, kids have to deal with the genetic cards their parents deal them. There is the possibility of a spontaneous mutation cropping up that MIGHT give the child a different look than the parents (there is a kind of dwarfism that is like that), it would be very rare.

2. mitochondrial DNA is not in the nucleus because it is found in the mitochondria. Mitochondrias are orgenelles - tiny structures within the cell - that are bascially little powerhouses. They provide the cell with energy.
Before fertilization, a woman's egg has lots of mitochondra in it. Men do have mitochondria, but their sperm do not - or at least only a very small amount (depending on who you ask). this is because sperm are highly specialized for one main objective: find egg, fertilize, provide DNA. So alll the mitochondria that anyone has have come strictly from mom. It's not that men don't have them, it's just that their sperm do not.

Incidently, it is thought that the reason mitochondria have DNA is that when life first began on earth, and we were all just a few cells floating in a primordial ooze, a cell that was destined to become all animal life on earth tried to eat a very primitive bacteria. But instead of becoming food, the bacteria somehow became part of the cells system, providing the benefit of energy for the cell.

I hope that helps you out! if you have any more questions, or if I just totally confused you, please email me at evilsciencechick (at) gmail (dot) com.

8/29/2005 05:49:00 PM  
Blogger Heather said...

Evil science chick! I think you have a future in publishing science for the masses!

8/29/2005 06:15:00 PM  
Anonymous Sharkey said...

Wow--post technical science questions on your blog, and the world responds. I love it.!

8/29/2005 08:39:00 PM  
Blogger Stephen (aka Q) said...

As for why anglo people don't have kids with asian eyes - well, kids have to deal with the genetic cards their parents deal them.

Which is to say that "racial" characteristics — shape of eyes, colour of skin, etc — are genetically determined. Geneticists sometimes seem to be saying something different than that, but it's just poor communication on their part.

But Mary P. is right, of course: there is only one human race. Geneticists say the differences within a race are greater than the differences between two races. And I'm willing to accept that.

Heck, I understand that there is more difference, genetically speaking, between a gorilla and a chimpanzee (where there is only 97% correspondence) then there is between a chimpanzee and a human being (where there is 98% correspondence). So I'm willing to believe that the differences between the human races are downright miniscule.

8/29/2005 09:12:00 PM  
Blogger Mary P. said...

Aginoth: Such a shame! I'm sure your children are doubly disapppointed... Hey. Maybe you can get some kind of refund on them (the kids, I mean) because half theirs are faulty, too!

Heather: thanks for the detailed response, but I confess I'm still not quite there yet. I understand the concept that certain "racial" characteristics are in fact found on a wide variety of genes. It's also quite clear to me that a caucasian woman isn't going to produce an "asian" child, because she doesn't have the genes to do that: but this seems to be restating my original point of confusion. Since we produce offspring with physical characteristics that fall within certain parameters, and these parameters are genetically determined, isn't this the same thing as saying "race" is genetically determined? No, not really, is the answer, but the distinction seems just a bit nebulous to me...

I'm sure this is my lack of acuity here, not your lack of clarity. I need to do some more thinking and reading, obviously. But thanks for your input!!

Evil Scientist Chick: WOW!! This is SO GREAT!! (Who is "Z"? Do I have a lurker?)

There is no way I can respond to your comments adequately within this teeny little box, but you will definitely be getting an email from me, you generous woman, you. Give me a little time to sort through your input, research a little more, and come up with some clearer questions. Sometimes you don't even know enough to formulate the questions that will bring you the information you need! I think that's where I'm at right now...

But I'm tremendously pleased you've offered your expertise to help out this non-scientific dabbler! Thank you! I'm also pleased to note that your spelling of "mitochondrial" confirms my suspicion that the book was spelling it incorrectly ("mitochrondrial"). Or perhaps there are two spellings?

Sharkey: Isn't it great? I'm delighted! (Can you tell??) I was mostly sharing something that interested me: I didn't really think anyone would actually come through with the straight dope! And a genetics grad student, no less - a bona fide expert! I love the internet!

Q: I guess what we colloquially call "races" are perhaps more accurately just "strains". We can, for example, interbreed without any difficulties. I'm still having some difficulties sorting it all out, though, I confess. Something to keep my brain busy next week when the deluge of toddlers returns. (How did that child come to fall in the toilet? Mary was too busy musing about racial distinctions and mitochondrial DNA...)

8/29/2005 10:03:00 PM  
Blogger evilsciencechick said...


never heard of that spelling.

mitochondrial. from mitochodria.

and you're welcome ;)

8/29/2005 11:23:00 PM  
Anonymous z. said...

me, me , me. I'm z. I've commented before i think.
It's just that when I read this entry I immediatly thought of evilsciencechick so I sent her an email and she came! and thought us things!
and that's it, I'm z.

8/30/2005 12:22:00 AM  
Blogger Mary P. said...

Hello, Z! Welcome. And thanks for sending ESC. (Hey, look at that acronym! Is that deliberate?)

8/30/2005 07:19:00 AM  

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