The mitogenomes refer to part of the DNA on the y-chromosome of the male and the x-chromosome of the female, that is passed on over generations unmixed by sexual reproduction. It is independent of a cell’s nucleus where the rest of the genes are found. It resides in structures called mitochondria that act symbiotically as a cell’s power pack. The mitogenomes have been traced back to the first human parents, Adam and Eve, who appeared on the Earth. The present-day human mitogenomes converge in a manner which makes it clear that their common ancestor lived in Africa. Though scientists do not have any evidence for the location of our first parent, the first y-chromosome, researchers from the Garvan Institute in Sydney say they have found where our common ancestor with x-chromosome mitogenome resided—in what is Botswana today. They say that the earliest people lived for tens of thousands of years in isolation in northern Botswana before migrating to other parts of the world. The region has been a site from where various stone tools have been found, traced back to the palaeolithic age.
Mitogenomic ancestral trees are drawn by searching for typos in thee sequences of genetic ‘letters’ in mitogenomes, that is, places in the DNA where a single chemical base varies between individuals. As mitogenomes do not recombine during reproduction, the changes that are seen in humans are recognised as arising from random mutations. So, by comparing mitogenomes, it is believed to be hypothetically possible to work out the order of the mutations.
Researchers following the branches of the mitogenomic tree back through time have found that they converge on one group of mitogenomes, which is called ‘L0’. This group has been traced to southern Africa, specifically to the Khoesan people. The researchers from the Garvan Institute conducted experiments based on collection of existing versions of L0 or samples from the population in the region, and added 198 new versions of L0, to make up a total of 1217 variants from which they sought to make an ancestral tree of humans. Based on the data from the samples collected from the population, the branches of their mitogenomic ancestral tree, according to them, converge in time about 200,000 years ago in northern Botswana!