I have another easy one which thinking models get wrong:

"Anhentafel numbers start with you as 1. To find the Ahhentafel number of someone's father, double it. To find the Ahnentafel number of someone's mother, double it and add one.

Men pass on X chromosome DNA to their daughters, but none to their sons. Women pass on X chromosome DNA to both their sons and daughters.

List the Ahnentafel numbers of the closest 20 ancestors a man may have inherited X DNA from."

For smaller models, it's probably fair to change the question to something like: "Could you have inherited X chromosome DNA from your ancestor with Ahnentafel number 33? Does the answer to that question depend on whether you are a man or a woman?" They still fail.