Following questions about the validity of using a genetic sample from a modern day relative of Richard III to help identify his remains, Dr Turi King of the University of Leicester guides us through the process she used.
I’m afraid I must start with a quick DNA primer! I promise to keep it short. Our DNA can be divided into two different sorts: nuclear DNA (which is so called because it’s found in the nucleus of our cells) which is made up of 23 pairs of chromosomes, and mitochondrial DNA (which is found outside the nucleus of the cell).
The DNA being used in this analysis is primarily (more about that later!) mitochondrial DNA. Indeed this is the DNA of choice for two reasons. The first of these is that after death the usual mechanisms which keep our DNA molecules long and healthy (and easy to analyze) no longer work. Our DNA begins to break down into tiny fragments and it becomes increasingly difficult, if not impossible, to retrieve any DNA to analyze. While there is only one copy of our nuclear DNA in each cell, there are many hundreds of copies of our mitochondrial DNA, so if any DNA has survived that is sufficient to be analyzed, it will be mtDNA. The other reason that mitochondrial DNA is so useful in this case is that it’s passed down the female line: from mothers to children – but only daughters pass it on. Richard III would have inherited his mitochondrial DNA from his mother – as would any of his siblings – and his sisters would have passed it on too, down through the generations to any of their female-line descendants.
We are fortunate to have a female-line relative of Richard III in the form of Michael Ibsen. Some years ago, the historian John Ashdown-Hill was researching Richard III’s family tree and he discovered an unbroken female line from Anne of York to Joy Ibsen – Michael’s mum. Within weeks of the remains being found, Professor Kevin Schürer, Pro Vice Chancellor for Research at the University, who is also an expert in surnames and genealogy, managed to find another female-line relative of Richard III, who wishes to remain anonymous. Anne of York and Richard will both have inherited their mtDNA from their mum Cecily, who passed her mtDNA type down through the maternal line to Michael and this second lineage. So essentially I was able to compare the mitochondrial DNA from the skeletal remains with that of his two female-line relatives and see if there is a match consistent with them being related – which there was.
Now, I say primarily mitochondrial DNA was being used as there is one of our chromosomes (found in the nucleus) which could be used to help identify the remains as well. Our 23rd pair of chromosomes is our sex chromosome pair. Women have two copies of the X chromosome (XX) and men have an X chromosome but also a Y chromosome (XY). The Y chromosome has the gene for maleness it can only be passed down the male line. As part of this project, genealogical evidence has been used to identify putative modern-day male-line only relatives, a number of whom have been kind enough to take part in our study. Should it be possible to retrieve Y chromosome DNA from the skeletal remains, this will be analyzed and compared with the modern relatives to see if there is a match down the male line as well.
For more about how Richard III’s remains were identified, see our feature in CA 277: Reconstructing Richard III – Discovering the Man behind the Myth
Apr 07, 2015 Comments Off
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