The Trouble with Autosomes

At Oxford Ancestors we do not offer autosomal testing.  This may surprise you. This is why.  The vast majority of our genes are carried on the chromosomes in the cell nucleus, other than the Y chromosome.  Their pattern of inheritance is complicated by the phenomenon of recombination whereby genes are shuffled at each generation.  Recombination is an essential process that has evolved to frustrate pathogens in their attempts to destroy us by making sure that children do not carry exactly the same genetic make-up as their parents. This is why even the worst pandemics do not kill everyone, as they certainly would if we were all genetically identical.   

  • Only 400 years ago you may have up to one million different DNA ancestors.

We receive our autosomes from both parents, who in turn have inherited theirs from our four grandparents.  As we go back through the generations, the number of ancestors doubles each time. Thus we each have eight great-grandparents, sixteen great-great-grandparents and so on.  Only twenty generations ago, which is about 400 years, we might have a million different ancestors each contributing some DNA to us. This situation is further complicated by genetic recombination making it impossible to know from which ancestor any particular piece of DNA has come. 

Beyond only a couple of generations into the past, the picture becomes hopelessly muddled and the only way to make apparent sense of it is to turn to extremely complex statistical interpretations with the attendant issues of gross oversimplification. Of these one of the most misleading is to believe that the world's population is divided into discrete racial or ethnic categories and to promote the idea that genetic testing is capable of assigning an individual's ancestry into one or a few of these groups.  This has been attempted many times in the past, most notoriously during the eugenics campaigns of the first half of the 20th century.  In my opinion, the claims of some testing organisations to derive an individual's ethnicity from a DNA test are not only fundamentally flawed from a scientific standpoint but also in danger, unwittingly perhaps, of carelessly repeating the mistakes of the eugenics movement by conflating genetics, race and ethnicity.