How To Find The Origin Of A Gene?

Question

[Pappu]

I am wondering how to determine in which organism a gene of interest first came into existence. It is possible to say from the phylogenetic tree or by other means?

Answer 1

[Chris Miller]

If you're looking at two modern organisms, the it most likely didn't occur first in either of them, but arose in a common ancestor. (convergent evolution being the rare, but possible exception)

[Pappu]

I am talking about prokaryotes.

[Chris Miller]

Unless you're taking horizontal gene transfer into account, the point stands.