In the wake of the post from earlier this week on the inbreeding within the House of Windsor (and current lack thereof), Luke Jostins, a subject of the British monarch, has a nice informative post up, Inbreeding, Genetic Disease and the Royal Wedding. This tidbit is of particular interest:
In fact, eleventh cousins is a pretty low degree of relatedness, by the standard of these things. A study of inbreeding in European populations found that couples from the UK are, on average, as genetically related as 6th cousins (the study looked at inbreeding in Scots, and in children of one Orkadian and one non-Orkadian. No English people, but I would be very suprised if we differed significantly). 6th cousins share about 0.006% of their DNA, and thus have about a 0.06% chance of developing a genetic disease via a common ancestor. Giving that the Royal Family are better than most at genealogy, we can probably conclude that the royal couple are less closely related than the average UK couple, and thus their children are less likely than most to suffer from a genetic disease. Good news for them, bad news for geneticists, perhaps?
That's an interesting flip side of aristocratic consanginuity, aristocratic cosmopolitanism. For example, Victoria of Sweden, the heir to the throne, has a Brazilian maternal grandmother and German maternal grandfather. Her father is by and large of the Northern European aristocracy,* but because he is of the House of Bernadotte his paternal lineage is rooted in a region on the alpine fringe of southwest France. The European aristocracy then serves as an interesting window into how cultural context can shape genetic variation. Also, a sidelight of curiosity is that Duchess of Cambridge (formerly Kate Middleton) has a maternal grandmother who comes from a lineage of laborers and miners. That's certainly a commentary on the possibilities for social mobility. There is a strong likelihood that a 20th century working class laborer will be the great-great grandparent of the British monarch at some point in the 21st century.