““If everyone on both sides of your family is tall, you are going to be tall. If half are tall and half are short, you have a 50//50 chance of being either tall or short. You also have the possibility of ending up somewhere in the middle.”” Confused? Apparently, so was this high school student. How did he develop such a muddled understanding of inheritance? Probably by attending class, reading his textbook, and doing his homework. His confusion, which was representative of many students who submitted essays to a national DNA Day essay contest, is quite common. In fact, in an analysis of 500 randomly selected essays by The American Society of Human Genetics (Shaw et al., 2008), 55%% of essays contained at least one misconception in genetics, and 20%% had two or more.
The most common misconceptions dealt with patterns of inheritance (clearly reflected in the quote above), genetic determinism, genetic technology, and the nature of genes. Those findings are consistent with an analysis of core genetics concepts on the 2000 National Assessment of Educational Progress. O'Sullivan et al. (2003) found that more than 90%% of students demonstrated only a partial or an unsatisfactory understanding of genes, mutations, genetic disease, and molecular genetics. Research in both model organisms and humans has dramatically improved our understanding of genetics over the past 30 years, so the poor grasp of fundamental principles displayed by our students seems counterintuitive.
What explains the gulf between where the research community is and where our students are? In a word, us —— the teachers of genetics. In spite of our dedication to our profession and a wealth of research about how students learn, we are falling short. In large part, this is because our curriculum has not kept up with the science. Genetics research has become ““genomic”” while curriculum and instruction are generally mired in an overly simplified conceptual framework that is 50 years old.
Until recently, I taught genetics to undergraduate students in both introductory biology courses and in a genetics course for majors, and, in general, I didn't do anything wildly out of the ordinary. For a college course, my classes may have been more inquiry-oriented and interactive than average, but my syllabus was very traditional. You would have recognized the typical sequence of content: transmission genetics followed by molecular genetics (our sole homage to the late 20th century) followed by Hardy-Weinberg and elaborations to evolution. The fact that I used current examples to illustrate these topics did little to convey to students the foundational changes that have occurred in genetics.
As I look at that sequence now, through the lens of 21st-century genetics information, I am not surprised that many (most?) of my students saw genetics as a science about individuals, not populations, and about discrete traits and simple ratios, not complexity. Should I have been surprised that many students tried to force-fit non-Mendelian inheritance into the familiar patterns we'd spent so much time on, even when I tried to elaborate (too late to matter, I think) from single-gene traits to continuously varying, multifactorial traits?
Happily, there may be a way to teach genetics that is more reflective of modern understanding and less apt to induce (or cement) students' misconceptions. If we began our instruction with common, complex traits, such as height, skin color, diabetes, and autism, we could capitalize on students' intuitive understanding that most traits do not exhibit the dichotomous (““either——or””) inheritance of the traits we typically emphasize, such as widow's peaks, cystic fibrosis, and pea color. In fact, most quantitative traits, such as height, blood lipid levels, and so on, have near-Gaussian distributions, and new experimental methods have been developed for studying genetic contributions to those traits. We could help students model how multiple genes (polygeny) contribute to continuously varying traits, which are also affected by environmental variables. Then we could introduce students to the rare single-gene traits (mostly disorders) that serve as elegant examples of Mendelian segregation and the familiar ratios that describe them.
This inverted sequence of concepts may help students think less deterministically, because they could recognize that many genes, not just one, contribute to complex traits. There is also complexity in monogenic traits, which we often ignore in our teaching. Polygeny, as we are discovering, accounts for much of the variable expressivity observed in many, perhaps most, ““single-gene”” traits. Moreover, genes acting epistatically may account for differences in penetrance that are observed in many traits. These observations of deeper complexity muddy the concept of ““monogenic”” as it is applied to traits.
An inverted approach would offer another benefit. It requires students to think in terms of populations, because continuous variation (in height, for example) is seen only when observing groups. (An individual does not have height or not; he or she has a particular, quantifiable height. The quantity of height is a product of genes and the environment.) Failure to reason at a population level is one of the major obstacles to students' understanding of evolution by natural selection. Phenotypic variation in populations is the substrate of selection —— with extraordinary genetic variation underlying that phenotypic diversity. Absent this insight, students should be forgiven for confusing an individual organism's developmental program with its place in an evolutionary life history.
The challenges of biology education extend beyond outdated genetics instruction, but hewing to a genetics curriculum that we know to be incomplete and misleading surely does not help. Hopefully, in another 10 years, students' DNA Day essays will show little evidence of the misconceptions that are so prevalent today.
The American Society of Human Genetics is planning to develop and test some of these curriculum ideas to see if genetics education can be brought into the 21st century. If you are interested in becoming involved in this project, please contact the author at the e-mail address given below (for more details, see Dougherty 2009).