Your illustrious medieval ancestors?

I caught a "Who Do You Think You Are" programme featuring Celia Imre the other day. She sought the origins of her son's radical politics and her own feminist feistiness in her ancestors. Here's what the program found for her:

"Imrie’s particular wish to uncover an ancestor to inspire her politically inclined son, Angus, unearthed a corker in her “eight-times grandfather” William, Lord Russell, son of the Earl of Bedford in the time of King Charles II. A leading Whig politician who truly had the courage of his convictions, Russell was such an intransigent defender of Protestantism and lover of constitutional liberty that he was accused of plotting to kill the King, and promptly beheaded.

"At Woburn Abbey, the Russell family seat, Imrie set out on the still more dramatic trail of Frances Howard, grandmother of the aforementioned William. A victim of one appalling dynastic marriage, and caught up in vicious courtly intrigues while trying to secure happiness in a second, she was packed off to the Tower of London with her new husband, accused of murder. Frances was eventually pardoned but history was not so forgiving."

So she had found her 'good genes' then? Not so fast, here's Richard Dawkins:

"For relationships as distant as third cousin, 2 x (1/2)⁸ = 1/128, we are getting down near the baseline probability that a particular gene possessed by [an individual] will be shared by any random individual taken from the population."

Celia Imre's “eight-times grandfather” William, Lord Russell, is nine generations separate from her and shares a relatedness of  1/512 = (2^-9). That distant relatedness could be greater if her lineage includes a degree of inbreeding - but it's unlikely to be more than 1/128 - Dawkins' rough figure for the genetic relationships of any two random ethnic English people.

So Celia Imre's traits for general lefty feistiness are certainly in her genes, but not through the good offices of those specific medieval ancestors.

More generally, you get a dilution down to 1/128 in seven generations. At four generations per century, you may assume that any specific traits of a specific ancestor more than 175 years ago (i.e. before c. 1839) have since been diluted out by Mendelian segregation and recombination. (Also more from 23andMe's reseaches here).

Genetic immortality? fuhgeddaboudit..