Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
5 online now:
Newest Member: popoi
Post Volume: Total: 915,821 Year: 3,078/9,624 Month: 923/1,588 Week: 106/223 Day: 4/13 Hour: 0/2


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Ratio of Deleterious Mutations to Beneficial Ones
Taq
Member
Posts: 9975
Joined: 03-06-2009
Member Rating: 5.7


Message 14 of 35 (719333)
02-13-2014 11:07 AM


Lower Threshold
In addition to the great Tweb thread, I have found this paper worth mentioning in these discussions.
quote:
Allen JM, Light JE, Perotti MA, Braig HR, Reed DL (2009) Mutational Meltdown in Primary Endosymbionts: Selection Limits Muller's Ratchet. PLoS ONE 4(3): e4969. doi:10.1371/journal.pone.0004969
Primary bacterial endosymbionts of insects (p-endosymbionts) are thought to be undergoing the process of Muller's ratchet where they accrue slightly deleterious mutations due to genetic drift in small populations with negligible recombination rates. If this process were to go unchecked over time, theory predicts mutational meltdown and eventual extinction. Although genome degradation is common among p-endosymbionts, we do not observe widespread p-endosymbiont extinction, suggesting that Muller's ratchet may be slowed or even stopped over time. For example, selection may act to slow the effects of Muller's ratchet by removing slightly deleterious mutations before they go to fixation thereby causing a decrease in nucleotide substitutions rates in older p-endosymbiont lineages.
Methodology/Principal Findings
To determine whether selection is slowing the effects of Muller's ratchet, we determined the age of the Candidatus Riesia/sucking louse assemblage and analyzed the nucleotide substitution rates of several p-endosymbiont lineages that differ in the length of time that they have been associated with their insect hosts. We find that Riesia is the youngest p-endosymbiont known to date, and has been associated with its louse hosts for only 13—25 My. Further, it is the fastest evolving p-endosymbiont with substitution rates of 19—34% per 50 My. When comparing Riesia to other insect p-endosymbionts, we find that nucleotide substitution rates decrease dramatically as the age of endosymbiosis increases.
Conclusions/Significance
A decrease in nucleotide substitution rates over time suggests that selection may be limiting the effects of Muller's ratchet by removing individuals with the highest mutational loads and decreasing the rate at which new mutations become fixed. This countering effect of selection could slow the overall rate of endosymbiont extinction.
In this paper, they looked at asexual endosymbionts which will suffer from genetic "meltdown" at even a greater clip due to Muller's Ratchet. What they found is slightly deleterious mutations built up there was increased negative selection for each additional slightly deleterious mutation. In other words, there is a threshold for the number of slightly deleterious mutations that a genome can incorporate. However, this doesn't result in extinction. Rather, each additional deleterious mutations is much more strongly selected against relative to the same mutations in previous generations. Sanford's model fails to incorporate increased selection as these mutations build up.
Edited by Taq, : No reason given.
Edited by Taq, : No reason given.

  
Taq
Member
Posts: 9975
Joined: 03-06-2009
Member Rating: 5.7


Message 17 of 35 (719372)
02-13-2014 5:52 PM
Reply to: Message 16 by NosyNed
02-13-2014 5:44 PM


Re: Neutral -- maybe not
I think this is leaving something out of the measurement. For living humans the mutations are somewhere close to neutral perhaps.
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.

This message is a reply to:
 Message 16 by NosyNed, posted 02-13-2014 5:44 PM NosyNed has replied

Replies to this message:
 Message 18 by NosyNed, posted 02-13-2014 6:33 PM Taq has replied

  
Taq
Member
Posts: 9975
Joined: 03-06-2009
Member Rating: 5.7


Message 19 of 35 (719377)
02-13-2014 6:50 PM
Reply to: Message 18 by NosyNed
02-13-2014 6:33 PM


Re: Neutral -- maybe not
But we are discussing this with a creationist who claims that "all", "most", "many" or some such portion of mutations are harmful.
They should be asked to supply evidence to back those claims.
It may be fair to say that a large percentage of the mutations that change amino acid sequence are deleterious, and that is often where the misunderstandings begin.
If we are born with 50 mutations, and 3% of the genome is translated into protein, this would mean that only 1 or 2 mutations occur in the coding portion of those genes. Each one would have about a 70% chances of changing the amino acid sequence, so about 1 per person. Already, we see that only 2% of mutations (at least for common substitution mutations) really have a chance of being seriously deleterious.
The real deleterious mutations are probably indels and recombination events that happen in coding regions. Indels that change the number of bases in a gene by a number indivisible by three will change more than just one amino acid due to a frame shift, as one example.
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.
My own suspicion is that this isn't the case. We are a somewhat promiscuous species, so there is selective pressure to keep our fecundity a little lower. The mutations that may be responsible for the rate of spontaneous abortions in humans are probably already present in the mother and father, and have been selected for. Again, this is my own speculation and I really don't have anything to back it up with just yet.
Edited by Taq, : No reason given.
Edited by Admin, : Fix spelling: promiscious => promiscuous

This message is a reply to:
 Message 18 by NosyNed, posted 02-13-2014 6:33 PM NosyNed has not replied

Replies to this message:
 Message 21 by Faith, posted 02-13-2014 8:01 PM Taq has replied

  
Taq
Member
Posts: 9975
Joined: 03-06-2009
Member Rating: 5.7


(1)
Message 33 of 35 (719471)
02-14-2014 10:39 AM
Reply to: Message 21 by Faith
02-13-2014 8:01 PM


Re: Neutral -- maybe not
It's all guesswork, isn't it?
No.
Seems to me I've seen threads where it's been affirmed by evolutionists that the vast majority of mutations are deleterious,
Then quote the posts.
You guys really don't know.
Yes, we do.
Between 80 and 90% of the human genome is accumulating mutations at a rate consistent with neutral drift. This is known.

This message is a reply to:
 Message 21 by Faith, posted 02-13-2014 8:01 PM Faith has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024