Can you explain this paragraph, please? (Biology)?

It says that parasites endosymbionts and organelles live inside an organism, so their evolution can not occur completely independently of this "host" organism. Over the long term then, these structures and the host structure tend to develop an interdependence on each other. Genes which perform the same functions in both can disrupt each other and harm this "system" as a whole, so these genes tend to be selected against. Eventually this may lead to the collapse of one or the other as the genetic information decreased down to the point where it is no longer viable.--- I hope that made more sense, anyway. Good Luck