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I know next to nothing about the dynamics of gene transmission (if someone does please shed some light), but it seems quite obvious that the less evolutionary p

by jkn 13y ago

I know next to nothing about the dynamics of gene transmission (if someone does please shed some light), but it seems quite obvious that the less evolutionary pressure you have against a gene, the more prevalent it will become. My intuition is that evolutionary pressure works against entropy. Without the pressure, the genome would evolve towards a state of maximum entropy, i.e. a particular mutation would reach a prevalence of about 50%. But of course there will always be some sort of evolutionary pressure.

Dylan16807 13y ago
I would expect more of a random walk. I suppose that very slowly genes would mutate by themselves, but as far as having certain genes spread, two kids multiplied by 50% chance equals the same number of people with the gene, generation after generation.
- jkn 13y ago
  Well I was actually thinking about mutations :) Let's consider a simplified model, where there are only two different bases (A and G instead of A, T, G, C) and assume that the probabilities of mutations A->G and G->A are the same. Let's consider a single base mutation[1]. No matter what the mutation probability is, and no matter what the initial distribution is, I expect that the population will converge to about 50% A and 50% G. I guess you would agree. Now if we make this very wrong model a bit less wrong by including the four base types A, T, G, C, we can expect that each allele will be found in about 25% of the population. And that is for single base mutations only. A mutation that depends on the precise value of 5 different bases would be displayed by a much smaller share of the population (1/4^5 = 0.1% I guess). Of course people don't get born with fully random genomes like that, the vast majority of these mutations would not yield a living embryo. But still, the intuition we can get from this is that without evolutionary pressure, a particular mutation will eventually be found in a fraction of the population that is inversely proportional to the complexity of the mutation (in most cases that would be far from the 50% of my initial intuition). No idea how close these layman's speculations are from the reality... [1] Such as the gene that determines the type of ear wax: http://udel.edu/~mcdonald/mythearwax.html http://udel.edu/~mcdonald/mythearwax.html

by jkn 13y ago

Dylan16807 13y ago

I would expect more of a random walk. I suppose that very slowly genes would mutate by themselves, but as far as having certain genes spread, two kids multiplied by 50% chance equals the same number of people with the gene, generation after generation.

jkn 13y ago
Well I was actually thinking about mutations :) Let's consider a simplified model, where there are only two different bases (A and G instead of A, T, G, C) and assume that the probabilities of mutations A->G and G->A are the same. Let's consider a single base mutation[1]. No matter what the mutation probability is, and no matter what the initial distribution is, I expect that the population will converge to about 50% A and 50% G. I guess you would agree. Now if we make this very wrong model a bit less wrong by including the four base types A, T, G, C, we can expect that each allele will be found in about 25% of the population. And that is for single base mutations only. A mutation that depends on the precise value of 5 different bases would be displayed by a much smaller share of the population (1/4^5 = 0.1% I guess). Of course people don't get born with fully random genomes like that, the vast majority of these mutations would not yield a living embryo. But still, the intuition we can get from this is that without evolutionary pressure, a particular mutation will eventually be found in a fraction of the population that is inversely proportional to the complexity of the mutation (in most cases that would be far from the 50% of my initial intuition). No idea how close these layman's speculations are from the reality... [1] Such as the gene that determines the type of ear wax: http://udel.edu/~mcdonald/mythearwax.html http://udel.edu/~mcdonald/mythearwax.html