The Mitochondria in many cells, are believed to have been bacteria that have been incorporated in the cytophysiology. Mitochondria first off, contain their own DNA, er, RNA. Additionally physiologically the mitochondrion, has an inner membrane and some organelle traits similar to prokaryotic cells. Lastly Mitochondria are the only organelle capable of replicating itself. <span />
In general, negative selection eliminates from the population very harmful changes to proteins that kill or stop reproduction. ... The authors also found a correlation between genes predicted to be under negative selection and genes implicated in certain hereditary diseases