The rRNA of chloroplasts fall into the cyanobacteria in these trees. These organelles also have a double membrane and heat shock proteins similar to bacteria. This makes it an ideal molecule to follow human evolution on a short time scale. Trees made from mito DNA show the deepest branches to be from Africans, and estimates of mutation rate suggest 100,000 to 200,000 years as the time of origin of our mitochondrial DNA in a single woman. The Y chromosome has a similar part of its DNA only inherited from father to son.
Mutations are much rarer here because it is nuclear DNA and also has no recombination.
Studies of Y chromosome polymorphisms show that very few Africans have a rare mutation seen in apes but not in other humans, suggesting that this mutation changed in the human lineage soon after it branched from the apes. This indicates an African origin. Trees made from the Y chromosome data also identify the 100,000 to 200,000 year time frame for the last common ancestor of our Y chromosome. The breakpoints between these regions represent unique historical events in mammalian evolution and they can be used to follow the exact evolution of the mammals. This will be more accurate than comparing sequences that have all diverged a similar degree and are not informative.