Mutations (Was: The Punctuated Clock)

p-m agapow agapow at
Sun Jun 15 01:39:04 EST 1997

Andrew Rambaut <andrew.rambaut at> wrote:
> Many mutations in protein coding DNA do not result in a change in amino
> acid due to the redundancy of code. Thus these occur despite natural
> selection as there is no phenotype to be selected. 

Maybe not - althought if i've interpreted Andrew in the wrong light, I
apologise in advance. However, this _is_ swinging off from the original

"Many mutations" is a fairly imprecise term. In fact only 25% of
substitution mutations (i.e. those that change nucleotide and hence the
codon it is within) result in samesense mutations, with the original and
mutated codons mapping to the same amino acid. A far greater percentage
result in an amino acid change that is chemically drastic. Hence, on the
level of the code _itself_ (not the emphasis), redundancy has been a
little overstated. (See Doolittle.)

Then you get to the very messy problem of how many amino acid
substitutions result in a functional change in the end product. As this
is close to the heart of neutral evolution debate, it is needless to say
that it is subject to much controversy. Gillespie noted that you could
find a supporter for any percentage from virtually 0% to 100%. And then
there's the recent observation of selection pressure on some synonymous
substitutions ... messy.

   crossref = {neurath79},
   author   = {Doolittle, Russel F.},
   title    = {Protein Evolution},
   pages    = {2--111},
   year     = {1979},
   editor    = {Neurath, Hans and Hill, Robert L.},
   title     = {The Proteins},
   volume    = {14},
   publisher = {Academic Press},
   address   = {New York},
   year      = {1979},
   author    = {Gillespie, John H.},
   title     = {The Causes of Molecular Evolution},
   publisher = {Oxford University Press},
   address   = {Oxford},
   year      = {1991},

paul-michael agapow (agapow at La Trobe Uni, Melbourne

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