Tongue rolling is a simple dominant trait

What actually happened

Alfred Sturtevant, a genuinely great geneticist, suggested in 1940 that tongue rolling was a simple Mendelian trait. By 1952 Philip Matlock had found identical twin pairs where one twin could roll and the other could not, which is fatal for a single-gene explanation since identical twins share their genes. Sturtevant himself wrote in 1965 that he was embarrassed to see it still in textbooks, and formally retracted it.

It stayed in textbooks anyway for another fifty years, because it makes a wonderfully convenient classroom exercise. The same is true of most of the classic "genetics lab" traits: attached earlobes, widow's peak, hitchhiker's thumb, cleft chin, and PTC tasting are all either polygenic or far messier than the tidy dominant/recessive story. A 2017 genome-wide association study of earlobe attachment identified at least 49 contributing genetic variants. If a teacher used your family to demonstrate inheritance with these traits, the demonstration was charming and the genetics were fictional.