Monday, January 30, 2006

The power of genetic mapping

There's always something interesting going on over at Nature Genetics. The editor's blog, Free Association, reports some notable publications each week. Today, they tell me the genetics of earwax.

Did you know that there are two types of earwax? (Wet and dry.) According to the authors, "The wet earwax is brownish and sticky," and the dry type is not, I guess. It sounds like the stuff you learn in school: do you have attached earlobes or unattached? Widow's peak or not? Can you curl your tongue? They're simple Mendelian traits, meaning that they are controlled by one gene with two possible identities. Either you have the "attached" earlobe gene, or you have the "unattached" earlobe gene.

Except that apparently this isn't the case. I know that eye color is inherited through a combination of genes, and so it's not always so straightforward. (I've heard stories from genetics teachers who told their students that blue eyes are recessive, so if both your parents have blue eyes, you are sure to have blue eyes. Then some brown-eyed student goes to the teacher in tears, thinking her mom had an affair, when really, it's more complicated than that.) But the hard thing to grasp is that there is no earlobe gene, attached or unattached. It's a lot more complicated than that.

Except in the case of earwax. These guys found the gene for a component of earwax, called cerumen. This is the stuff that makes earwax wet and sticky. My earwax, like that of people from European or African descent, is wet and sticky. Eww. But apparently most people of Asian descent (M?) have dry earwax, because of a single nucleotide polymorphism in the cerumen gene. That is, in the cerumen gene sequence (made up of many A, T, C, and G nucleotides), one nucleotide is different in sticky earwax people and in dry earwax people. ONE single nucleotide.

And it looks like that one nucleotide can have a profound effect on the cerumen protein. The nucleotide change causes an amino acid change in the protein (Gly to Arg, a significant difference), and for some reason that has an effect on protein expression. (Probably, the amino acid change causes the protein to not fold properly, and so it gets degraded.) So basically, because Asians have this single nucleotide polymorphism (SNP), they don't have any cerumen to make their earwax sticky. Lucky ducks.

1 comment:

  1. I just read that, and personal experience confirms that it is true. At least, mostly. :-)

    ReplyDelete