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I've polled my students for several years about the false "Mendelian" traits that their high school biology teachers used as examples. There are SO MANY teacher resources that have false information about human traits. Earlobes, widow's peak, tongue rolling, none are Mendelian.
This semester I asked them to share these examples on a discussion forum. One student wrote, "I find it super interesting that we all had this similar experience, and it isn't even true."
For teachers, please check out the "Myths of Human Genetics" site by John McDonald from @UDelaware. This is an outstanding resource.
Also, please be aware that popular "examples of genetics" sites online contain false information. And the NLM "OMIM" (Online Mendelian Inheritance in Man" resource is not a *list* of Mendelian traits, and a trait having an OMIM entry does not indicate it is Mendelian.
It's understandable that teachers want visible examples of Mendelian inheritance that are not disease. But it's biologically important that a Mendelian inheritance pattern is so rare for common externally visible traits. It is an outcome of natural selection.
I suggest John McDonald's solution for teaching these, which relies on coat color variants in domesticated animals. Again, the fact that domesticates have genes of large effect on pigmentation is a lesson about evolution; in this case humans selected breeds intentionally.
Asparagus urine and cilantro tasting are not terrible, although they are also not great -- each has too much environmental variance to make them conform to Mendel's laws very well on a pedigree. Earwax consistency and alcohol flushing reaction are not terrible either....BUT
..even these traits that actually are strongly influenced by variation in a single genetic locus STILL will not reliably illustrate dominant and recessive in your students and their relatives. And that's an important biology lesson. Environmental variance and other genes matter.
Bottom line: The excessive focus on Mendel's laws (I'm looking at you, Common Core and AP Biology) is resulting in students failing to understand biological variation of ALMOST EVERY HUMAN PHENOTYPE. Misinformation and misconceptions are filling the gaps.
