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Re: Rconstructing DNA (was Re: Dino-fuzz found in amber?)
On Sat, Sep 17, 2011 at 2:38 AM, Tim Williams <email@example.com> wrote:
> It would take too long to explain why.
Well, it seems that it would take longer to explain you why my
assertion is a reasonable one..
> Why do you assume that the choice of base in the chicken is ancestral?
Excuse me. Where did I have assumed such a thing? I'm not assuming
chicken sequence as ancestral. What I'm assuming is that chicken and
T-rex sequences are homologous, are derived from a common ancestral.
Lets use parsimony for simplification.
T-rex second codon must be: TTA, TTG, CTT, CTC, CTA or CTG for leucine.
Since we have CTT for chicken, by parsimony, we infer that the T-rex
and chicken common ancestral codon would have a C in the first
position. So no additional evolutionary step is required. If ancestral
was supposed to have T in the first position, an additional step of
change from T->C in chicken will be required.
Of course, comparing this just two sequences, using only parsimony -
since the peptide sequences is identifical, we will endup assuming
that the common ancestral will have the chicken sequence. We could do
it, and assign a margin of error due to mutation fixation rate.
Lets say that the mutation rate is constant over the time and along
the sequence of, say, 1 SNPs per 100 mya. In this case, about 4 SNPs
> The "_T. rex_" peptide sequence just happens to show 100% match to the chicken
> peptide sequence....