DNA of Kings? – Why you may not inherit the DNA of your Ancestors.
Many of us will have watched the episode of ‘Who Do You Think You Are?’ where actor Danny Dyer discovers, to his and our astonishment, that he’s a direct descendent of King Edward III. But does that mean Danny’s blood runs blue? Does he carry the DNA of Kings? Our genealogist, Andy Robson, explains why it is actually extremely unlikely that Danny shares any DNA at all with his Royal ancestor.
How DNA is inherited
To begin, let’s try to recall your school biology classes. Everyone has 46 chromosomes, arranged in pairs twisted together; the famous ‘double helix’. 22 of these pairs are termed the Autosomals. The remaining pair are the ‘sex’ pair and define whether a person is male (XY) or female (XX). All of these have a part to play in DNA analysis to determine ancestry.
The Autosomal Pairs are something of a melting pot. Each of our parents passes around half of their DNA to us. So, our father, for example, has around 7,400cM worth of matches in his total genetic make-up. Around 3,700cM of this will come down to us. But around 3,700cM will not.
If fact, it’s even more complicated than this! DNA is not passed by any kind of strict rule. Instead, it is a somewhat random process. So, we don’t actually get 50% of our DNA from each parent. Rather we might get 48% from one and 52% from the other. As we move back through the generations, this effect is amplified, some DNA being preserved, other DNA being reduced or even eliminated.
Y-DNA carried in the Y chromosome of the ‘sex’ pair though is passed down the direct male line from father-to-son. Although Y-DNA represents only a tiny fraction of our overall lineage, it is important in that it remains largely intact when it is passed down through the generations.
So, what does this mean for Danny?
It has been calculated that if you go back to your 4x Great Grandparents (all 64 of them), around half of them will either not have contributed anything to your DNA at all, or will have contributed so little that it cannot be detected! Now let’s go back much, much further. In Danny Dyer’s case to his 22 x Great Grandfather. The number of Grandparents doubles with each generation so If my maths is correct then King Edward was just one of Danny’s 16,777,216 22x Great Grandparents!
So, sadly, while Danny may be descended from Kings, any DNA contribution from them would be so diminished as to be undetectable or more probably, simply non-existent.
Note, however, that if Danny had been a descendent of King Edward through the direct male line (the link is actually through his 11x Great Grandmother, Catherine Cromwell*) then there would have been a detectable link through his Y-chromosome which is passed down intact from father to son. Although the Y-chromosome mutates over time, this is at a slow and relatively predictable rate and so the Y-DNA link to King Edward would still be present.
This feature of the Y-chromosome allows direct-line male ancestors to be traced back Centuries or even Millennia. There have been fascinating studies recently about descent from famous Scottish and Welsh Kings and Warlords. It is the Y-DNA that is being plotted in these.
If you’d like to know more about DNA and where it may be taking us from a genealogical standpoint my reading recommendation is ‘Tracing your Ancestors using DNA – a guide for Family Historians’ published by Pen&Sword Books. This is a series of essays written by experts in the field and edited by Graham S. Holton. Very knowledgeable, very comprehensive, but also easy to follow.