A survey and evaluation of human genetic traits used in classroom laboratory studies.

Twenty-six selected introductory biology and genetics laboratory manuals were examined and were found to include 57 human "inherited" traits as examples for classroom study. Forty-three of these 57 traits are included in McKusick's catalog of human inherited characteristics, Mendelian Inheritance in Man. Of these 43 traits, 26 are annotated with an asterisk, indicating that their modes of inheritance are well documented, while 17 traits are not so annotated, suggesting uncertain mechanisms of inheritance. Fourteen of the 57 traits are not found in McKusick's catalog, implying that they may not be inherited traits at all or that their modes of inheritance may be polygenic. Current literature also suggest that certain traits included in the McKusick catalog may, in fact, not have a genetic basis. Notable examples of such questionable traits are handedness, hand clasping, and tongue rolling. Clearly, a need exists for reliable morphological and easily detected biochemical human genetic traits for use in classroom instruction. Authors preparing instructional manuals for introductory biology and genetics laboratory studies should carefully select the traits with which they illustrate human inheritance. A first requisite for selection of such characteristics must be conclusive evidence that the trait does, indeed, have an established genetic basis. Additional criteria for selection of such traits are also discussed.