Using Human Pedigrees to Teach Mendelian Genetics

Abstract

Radical Genetic Findings Overturn Mendel's Laws. article bearing this headline (Raeburn 1989) reported on an address given by medical geneticist Judith Hall at a July 1989 conference at Jackson Laboratory in Bar Harbor, Maine. I was at Bar Harbor and heard Hall's challenging presentation. She discussed the phenomenon of which is germline specific modifications which produce functional differences in expression of genetic material . . . depending on whether the genetic material comes from the mother or the father (Hall 1989). Differential activity of maternally and paternally derived chromosome regions has been reported in mice (Cattanach & Kirk 1985) and more recently in humans (Knoll, et al. 1989). Among the examples of imprinting that Hall discussed is the difference in syndromes produced by the deletion of a small segment of the long arm of chromosome 15 in humans. If the deletion is inherited from the father, the resulting array of symptoms is referred to as Prader-Willi Syndrome. If the deletion is maternally inherited, it results in a different set of associated symptoms, Angelman syndrome. While such a discovery is dramatic and seems to be an exception to classical Mendelian thinking, keep in mind that, contrary to the sensational headline, Mendel's laws have not been overturned. Imprinting appears to be an exception to classical Mendelism just as linkage is an exception to independent assortment, but the more than 4,000 Mendelian genetic conditions that have been identified in humans argue for the continued viability of Mendelian genetics. McKusick (1969) states, The chief method of genetic study in man is the observation of patterns, that is, the patterns of distribution of genetic traits in kindreds. Similarly, Fuhrman and Vogel (1983) state, A detailed gives us the necessary basic information for all further genetic considerations. Despite the many technological advances of the last 20 years, pedigrees of Mendelian traits remain the most basic analytic tool of human and medical geneticists. Indeed, many of the advances in technology have enhanced the usefulness of the method, allowing one to trace, for example, the inheritance of unique DNA markers throughout a human kindred. It was an advance of this type that led to assigning the gene for Huntington's Disease to human chromosome number 4. Human pedigrees are also useful tools in the classroom, where they can serve to introduce students to the basics of Mendelian principles of inheritance. challenges afforded the student by analysis can be as rigorous and demanding as those associated with the analysis of data collected from investigations involving experimental organisms. Moreover, many beginning biology students will identify personally with the analysis of human pedigrees, where they may not have their interest piqued by the study of guinea pigs, drosophila, maize (Indian corn) or pea plants. purpose of this article is to present suggestions for using human pedigrees in the classroom and to provide a pedigree that can be used to make a transparency for overhead projection or a spirit master for preparing multiple copies for classroom distribution. generic has been prepared in a manner that can be readily modified by the instructor to provide students a host of variants to analyze.