Genotype difference, phenotype difference and phylogeny (1 Viewer)

Looking at threads in this forum someone not being expert in this area (like me) could come to the conclusion, that genotype differences not always reflect taxonomic differences. But why should they ?
Actually they reflect only difference in TIME elapsed from separation (number of accumulated mutations dependent on time), but taxonomic difference is determined by phenotypes ...
Difference in given DNA sequence doesn't determine difference in phenotype proportionally ...

locustella said:

Looking at threads in this forum someone not being expert in this area (like me) could come to the conclusion, that genotype differences not always reflect taxonomic differences. But why should they ?
Actually they reflect only difference in TIME elapsed from separation (number of accumulated mutations dependent on time), but taxonomic difference is determined by phenotypes ...
Difference in given DNA sequence doesn't determine difference in phenotype proportionally ...

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Maybe -- Maybe not. Which part of the DNA is investigated does have a lot to do with the correlation, or lack thereof, between phenotype and genotype. What if the one gene you are investigating is the single gene that has 3 mutations causing the whole phenotypic difference?

And on the flip side of that coin: what if the difference in phenotype is a relatively trivial one, one that can be achieved by a couple of mutations, then the question really is: is there any reproductive isolation due to this phenotypic difference, or is a better predictor the overall DNA difference averaged over large parts of the genome, because on average, longer time correlates with reproductive isolation?

Niels