
Last week, we talked about gene duplication and looked at some simulation results. For starters, I was just simulating a random walk in the number of genes. The probability of adding a gene (taking a step ‘up’) remained the same, but I varied the probability of losing a gene (taking a step ‘down’). And I prevented the number from ever getting to zero or lower. You can see the results to the right (click for a bigger version). When the probability of losing a gene is 10x higher than gaining (purple/darkest line), the number of genes (averaged over 128 trials) basically stays at 1. No big surprise there; any time a gene is gained, we’d expect to lose it again very quickly before another one is added. Conversely, when the probability of losing a gene is 10x lower than gaining (yellow/lightest line), the average number of genes just keeps on growing; again, not a big surprise. But when the probability of gaining and losing a gene is the same (green/intermediate line), the average number of genes creeps up, possibly leveling off somewhere just above 10. You’d probably expect some kind of equilibrium, but would you have predicted that’s where it would be?
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