The University of Leicester’s Department of Genetics is famous as the birthplace of DNA fingerprinting, discovered here by Professor Sir Alec Jeffreys in 1984 and widely used by governments and law enforcement since then. However, a different approach was required when the Department of Genetics’ Dr Turi King set out to investigate possible connections between two people born five centuries – and 18 generations – apart.
Most of our DNA exists within the cell nucleus but a small amount exists within mitochondria, small organelles whose function is to convert chemical energy (from food) into a form that the body can use. Mitochondrial DNA (mtDNA) is a small loop of DNA which is transmitted from mother to child and is therefore very useful in tracing female lines of descent.
The mitochondria in sperm cells are destroyed as part of the fertilisation process so there is no combination and mtDNA is transmitted unchanged from mother to child. As long as the female line remains unbroken, the mtDNA remains constant, barring small naturally occurring mutations. This means that Richard III, Edward IV and Anne of York all had the same mtDNA – from their mother, Cecily Neville – and as long as Anne’s daughters continued to produce daughters of their own (highly likely in an age when eight to ten children was common!), the mtDNA will have been passed down those lines of descent.
Another advantage of mtDNA is that there are many mitochondria within each cell. DNA starts to degrade after death but with so many copies of the mtDNA, there is a good chance of being able to sequence it – even after 527 years.
Consequently, if the remains found at Greyfriars are indeed Cecily Neville’s son Richard III, the mtDNA present should match that of her great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandson Michael Ibsen – because there are no males in the line of descent from Cecily to Michael.
The survival of usable DNA depends less on the age of the remains than on the quality of the soil in which they lie (eg.acidity).
After careful excavation from the Greyfriars site, the skull, the lower jaw and one femur (thigh bone) from the skeleton were placed for safe-keeping in the clean room in the University’s Space Research Centre – normally used for the construction of spacecraft components. Due to their preservation, the teeth offered the best hope of intact mtDNA but the femur was kept as a back-up source.