Selfish chromosomes, evolution, and arpiar saunders

I wanted to give a shout out to Arpiar Saunders, not only because he's a friend of mine but because he is the co-author of a really good article out in Science this week about chromosomal evolution with the intimidating title "Centromere-Associated Female Meiotic Drive Entails Male Fitness Costs in Monkeyflowers". Although the old no-one-really-says-this-but-it-fits-my-point saying about Science is that "if it makes it in Science, it's got to be interesting" is not alway true, and although female meiotic drive may not be particularly self-explanatory as to why it's so interesting, I'll try to convince you that it's actually a really cool addition to how we think about evolution and selfishness in the biological world (I apologize, Arpy, or anyone who actually understands this science better than me, for the butcherin' that's a-comin').

First, we need a quick reminder about high school biology and cell division. So, most cells in your body have two copies of each chromosome (these are the little Xs that your genes hang out on, and we have twenty three different chromosomes), one that came from your dad, one from your mom. combined when your parents bung. When you, as a biological, adult, are going to combine your genes with another person's (what was once called "sex"), you are only going to pass on one of those two copies to your sperm or egg, which each only have one copy of each chromosome (then they get together so that the fertilized egg, later "zygote," has two copies of each chromosome).

So Mendel (papa bear of genetics) assumed that each trait in genetics had an equal probability of being passed on. In modern genetics, this would mean that each of the two chromosomes, each containing a bunch of genetic info, has an equal opportunity of being passed into the sex cells. Then natural selection determines which of these genes (which are sitting on chromosomes) is best "fit" to the environment, and those combinations of genes that are most successful in the environment reproduce more and make more copies of those genes, and presto, evolution.

The traditional focus of evolutionary theory, then, has been put mostly into the arena of adult fitness, or animal performance. What really matters though, is what genes get passed on. So, what Arpiar Saunders and Lila Fishman (at the University of Montana) studied was how genes can exploit and be successful at a very different moment in evolution. Using some genomics voodoo, they tracked a gene that preferentially gets passed on during female meiosis (i.e. makes it more likely that its chromosome gets passed on versus its homologous chromosome in the same cell). Most interestingly, however, individuals who were homozygous for this gene (they had two copies of the same gene, one on each chromosome) showed decreased pollen viability. So, boiled down to a tiny nugget of information, this is an example of how genes can compete on the molecular level, and how certain genes can become relatively prevalent in a genetic population, despite decreasing overall performance of the organism they're hitching a ride in. Selfish douchebags.