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Author Topic:   Ratio of Deleterious Mutations to Beneficial Ones
NosyNed
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Posts: 8996
From: Canada
Joined: 04-04-2003


Message 16 of 35 (719371)
02-13-2014 5:44 PM
Reply to: Message 15 by NoNukes
02-13-2014 5:11 PM


Neutral -- maybe not
The fact is that most human mutations are somewhere close to neutral with respect to fitness. We know this because every human has mutations.
I think this is leaving something out of the measurement. For living humans the mutations are somewhere close to neutral perhaps.
But what about the 50% or more who don't survive the first few weeks of gestation? We haven't measured how much of those failures to survive is due to mutations so we don't know but it might well be that 50 % of the mutations off the top are deleterious.
After that initial ruthless selection we are then left with neutral, mildly deleterious and beneficial.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 18 of 35 (719375)
02-13-2014 6:33 PM
Reply to: Message 17 by Taq
02-13-2014 5:52 PM


Re: Neutral -- maybe not
A much better way to put it is that 80-90% of our genome is accumulating mutations at a rate that is consistent with neutral drift which would indicate that the vast majority of mutations do not affect fitness to the point that natural selection can see the difference.
That may be perfectly fine as one way of looking at it. And I find that a very interesting number. Thanks for it.
However, I think the context here is the rate of all kinds of mutations at all points. That means not just in the germ line and not just in the living individuals we may study.
From a reasonable evolutionary perspective it is valid to say that the mutations mostly hover around neutral which your neutral drift information supports.
But we are discussing this with a creationist who claims that "all", "most", "many" or some such portion of mutations are harmful. And from one perspective they may be right. Maybe (I think we don't have the numbers ) harmful mutations are actually in the majority.
Maybe it is worth pointing that possibility out too. This now leads to the recognition of the effect of selection. If the failure of a large percentage of pregnancies is actually due to mutations it demonstrates the power of selection to weed out those mutations.
Without knowing the actual numbers it is clearly possible to conclude that if an individual starts off with a genome that contains a very seriously bad mutation they will obviously not pass the selection filter. In the case of humans we manage to thrive while loosing about half of all fertilization to spontaneous abortions. Since we can manage with that it seems clear that very deleterious mutations can be in the majority and still not be a long term threat to a species and not be of any concern to the evolutionary process.
Edited by Admin, : Fix quote.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 23 of 35 (719387)
02-13-2014 8:26 PM
Reply to: Message 20 by Faith
02-13-2014 7:56 PM


Selected against
Since we're all guessing, my guess would be that in some sense the vast majority are deleterious but not severe enough to be selected against and those mutations are going to get passed on along with all the other alleles, and any deleterious effects are going to show up generations later.
Actually if they are not selected out then they are, for practical purposes, not deleterious. If they show up generations later and they have finally reached a number or an environment were they are, for practical purposes, deleterious and are selected out.
Remember, many mutations are both deleterious and advantageous. The phenotype of a Swahili cattle herder is very advantageous in southern Africa but very deleterious in the high arctic.

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 Message 20 by Faith, posted 02-13-2014 7:56 PM Faith has replied

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