MikeFerrara:
If we're talking about dice, each combination is just as likely as another with each throw. Does it really work that way with DNA?
Wow, I thought the mods had removed the thread - it disappeared there for a while. To think, instead of entertaining my lady friend I coulda hung out here all weekend
Any how, mutations of DNA are a little more complex then dice.
Where/where mutations happen is completely random, so in that context mutations are like dice - 100% random. But this doesn't necessarily follow through to that actual accumulation of mutations in a species. When a mutation occurs there are a few "fates" for it:
1) It can be repaired. In fact, our DNA repair enzymes fix most mutations before they can be passed onto our offspring.
2) The mutation can be "silent". This is just a fancy way of saying that although the DNA has been mutated, the mutation itself has no effect on the proteins produced by the organism, and hence has not actually changed the organism. In human only 10-15% of our DNA even has the potential to be mutated in such a way as to change the organism. As such, the large majority of the mutations (i.e. 85-90%) which do occur, occur in regions where they don't have any effect what-so-ever. And even those which do occur in the "sensitive" 10-15% of our DNA only have a modest chance of actually altering the organism.
3) The mutation can be fatal. Meaning that whoever gets it dies, and hence it is not passed on. More often than not, these mutations get screened out before birth, as they are lethal before the fetus even reaches birth. In the case of humans, only about 50% of pregnancies reach birth (not counting abortions), and a large portion of those which are spontaneously aborted are done so because they carry a lethal mutation.
4) The mutation can be fairly harmful, but not lethal. These mutations CAN be passed down generation-to-generation, but more often than not are removed from a species within a couple of generations.
The mutations which do change the organism, and get through this gauntlet of selection, have a range of effects. Some will be beneficial, some will be a little bit bad, and some will have no discernible advantage or cost. What happens to these mutations is determined by various evolutionary forces (i.e. natural selection, sexual selection and genetic drift).
So mutations are like dice, in that they are random, but unlike dice, in that only some outcomes can occur.
Bryan
