I don't konw how the word(do) is used in some context.

Hi Seonwoong,

Welcome to the Forum.

While I read some article, I got a problem with understanding caused by my short vocabulary studing span.

Here it is,

"Mitochondrial genomes have many fewer genes than do the related eubacteria from which they are thought to be descended."

My problem, in here, is "do". I'm wondering whether there is some usage of "do" like this and whether I can change the location of this word, at last, The meaning of "do" in this context.

You could say Mitochondrial genomes have many fewer genes than the related eubacteria ( from which they are thought to be descended  ) do (have)."

Does this help you to understand more easily? 

Best wishes, Clive

Hi,

Is this for the sake of emphasis? Hyperbation?

To some extent, but not really. It's just a way to avoid a long separation between the subject and the verb, in a long clause. It's a normal feature of written more than of spoken English, because an 'educated' person can write his sentence more carefully than if he is speaking.

Best wishes, Clive