On Neurotopia, Scicurious offers a refresher course on mitosis. This vital process occurs every time a cell divides, as centrosomes pull apart replicated chromosomes with microtubules. Normal cell mechanics limit this "molecular tug of war" to about 50 iterations, meaning we can't keep splitting chromosomes forever. But we can use meiosis make some babies. On Gene Expression, Razib Khan explains that the X chromosome is relatively scarce since males only carry one copy of it, while all other chromosomes travel in pairs. This makes the X chromosome "more susceptible to stochastic fluctuations in frequency such as random genetic drift," causing it to exhibit "greater between population variance" than the genome as whole. And on Not Exactly Rocket Science, Ed Yong stands up for X's puny boyfriend the Y, a chromosome that once jettisoned "around 97% of its original genes." These days, the human Y chromosome is definitely up to something, having racked up 310 million years worth of evolutionary change in the 6 million years since chimps and humans shared a common ancestor.
Links below the fold.
- Mitosis on Neuroropia
- The tales that the X chromosome tells on Gene Expression
- X chromosome marks the spot, again on Gene Expression
- Renovating a runt - the extreme evolution of the Y chromosome on Not Exactly Rocket Science