[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Mice given bat-like forelimbs through gene switch

So there are still molecular biologists who call similarity "homology"...
no, people. No. That's not what homology means.

Then fill me in. What does 'homologous' mean? If all 16S rRNA genes have a shared ancestry (and they do), why are they not homologous?

"Degree of similarity" and "(degree of) homology" are not the same. If you want to say "38 percent identical", then say "38 percent identical" and not "38 percent homologous".

Phenetics is based on overall morphological similarity, which doesn't work for prokaryotes (at least not for higher-level classification) where external physical characteristics are a poor indicator of shared ancestry (as assessed by 16S rRNA sequence identity). Physical characteristics are encoded by genes, and genes are prone to rampant lateral gene transfer. Cladistics would also not apply, for the same reason.

Neither phenetics nor cladistics are limited to morphology. This is the first time I come across someone believing that they are.

The phylogeny of archaea and bacteria is based principally on the 16S rRNA gene. Using the phylogeny of the 16S rRNA gene as the basis for prokaryote classification (and life in general) is neither phenetic or cladistic. This applies to any molecule-based phylogeny.

All of them are cladistic. Except those that were made with a distance-based method like neighbor-joining or (historically) UPGMA -- those are phenetic.

To be honest, I don't know to what extent PhyloCode could (or does already) apply to the classification of bacteria and archaea.

It allows you to name clades and define those names... just like elsewhere.