The Amish polydactylism example stems from a larger disorder, Ellis-van Creveld disease. This is the result of extreme genetic drift, specifically called the “founder effect”. The founder effect happens when there is limited genetic variation “when a new population is established by a very small number of individuals from a larger population”.
It is still not the result of dominant genes being passed along, but rather the recessive ones are given to children by both parents and therefore seen more frequently.
This link explains the Amish example and all I’ve mentioend above quite well:
http://www.pbs.org/wgbh/evolution/library/06/3/l_063_03.html
(I’m having trouble including the links, not sure why)
Can we assume the founder effect is the culprit in the DR? But then also, is polydactylism in the DR a result of a larger disease as seen in the Pennsylvanian Amish?
I’d still like to know if there has been an academic study of some sort.