"Where do we come from?" This has been one of the fundamental questions asked by humans for thousands of years.Physical anthropologists have been providing an answer for over a hundred years by studying morphological characteristics, such as skull shape, of the fossilised remains of our human and proto-human ancestors. For the last 15 years or so, molecular anthropologists have been comparing the DNA of living humans of diverse origins to build evolutionary trees. Mutations occur in our DNA at a regular rate and will often be passed along to our children. It is these differences (polymorphisms) that, on a genotypic level, make us all unique and analysis of these differences will show how closely we are related. However, different approaches used by molecular and physical anthropologists have led to opposing views on how modern humans evolved from our archaic ancestors. Mitochondrial DNA is present inside the nucleus of every cell of our body but it is the DNA of the cell's mitochondria that has been most commonly used to construct evolutionary trees.
Mitochondria have their own genome of about 16,500 bp that exists outside of the cell nucleus. Each contains 13 protein coding genes, 22 tRNAs and 2 rRNAs. They are present in large numbers in each cell, so fewer samples are required.
They have a higher rate of substitution (mutations where one nucleotide is replaced with another) than nuclear DNA making it easier to resolve differences between closely related individuals.
They are inherited only from the mother, which allows tracing of a direct genetic line.
They don't recombine. The process of recombination in nuclear DNA (except the Y chromosome) mixes sections of DNA from the mother and the father creating a garbled genetic history.
Happy Mother's Day and if you are saying it with flowers remember to thank your mothers for their Mitochondrial DNA and your genetic lineage.
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We are who we think we are!
Something my Mother used to say:
You can't cry over spilled milk!!
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