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Author Topic:   Introduction to Genetics
Dr Jack
Member (Idle past 363 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 43 of 236 (680846)
11-21-2012 1:22 PM
Reply to: Message 41 by crashfrog
11-20-2012 7:09 PM


Re: QUESTION 9: "Junk DNA"
3) "Bulking out" one's genome with genetic "noise" serves to minimize the effect of frameshift mutations by spreading out the genes.

How does that work then? A frameshift mutation is only a frameshift mutation if it shifts the frame - i.e. if there is a insertion or deletion in the coding region. How will putting them further apart influence that?


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 Message 41 by crashfrog, posted 11-20-2012 7:09 PM crashfrog has responded

Replies to this message:
 Message 44 by crashfrog, posted 11-21-2012 2:11 PM Dr Jack has responded

  
Dr Jack
Member (Idle past 363 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 48 of 236 (681020)
11-22-2012 4:45 AM
Reply to: Message 44 by crashfrog
11-21-2012 2:11 PM


Re: QUESTION 9: "Junk DNA"
Well, if you pack each gene with introns, and every base has an equal chance of being an indel, then you increase the chance that a frameshift mutation will be canceled out by another one, downstream.

I don't follow; introns are excised by the gene machinery - indels in them make no odds corrected or not - it's only indels in exons that are relevant and the chance for them to occur remains constant regardless of how many introns you insert or how widely spaced genes are on the genome.


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 Message 44 by crashfrog, posted 11-21-2012 2:11 PM crashfrog has not yet responded

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 Message 50 by PaulK, posted 11-22-2012 5:23 AM Dr Jack has responded

  
Dr Jack
Member (Idle past 363 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 49 of 236 (681022)
11-22-2012 4:53 AM
Reply to: Message 45 by crashfrog
11-21-2012 2:12 PM


Re: QUESTION 9: "Junk DNA"
And by "purifying selection", you mean "natural selection against mutations"?

Not quite, purifying selection is the removal of harmful alleles from the population, not simply the removal of mutations. Neutral and positive mutations will persist.


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Dr Jack
Member (Idle past 363 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 51 of 236 (681040)
11-22-2012 7:56 AM
Reply to: Message 50 by PaulK
11-22-2012 5:23 AM


Re: QUESTION 9: "Junk DNA"
Introns don't reset the frame; you can get codons split between two exons.

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Dr Jack
Member (Idle past 363 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 54 of 236 (681051)
11-22-2012 8:45 AM
Reply to: Message 53 by PaulK
11-22-2012 8:32 AM


Re: QUESTION 9: "Junk DNA"
It seems to be referring to something like this (unfortunately the paper's in Russian which I can't read). I can see that against chemical mutagens non-coding DNA could be protective (although I doubt it would be against radiation) but I don't see how it's particularly relevant to indels (thought to occur primarily through slippage during replication).

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