‘Untangling Sickle-cell Anemia and the Teaching of Heterozygote Protection’

Abstract

Introductory biology textbooks often use the example of sickle-cell anemia to illustrate the concept of heterozygote protection. Ordinarily scientists expect the frequency of a gene associated with a debilitating illness would be low owing to its continual elimination by natural selection. The gene that causes sickle-cell anemia, however, has a relatively high frequency in many parts of the world. Historically, scientists proposed and defended several alternative theories to account for this anomaly, though it is now widely recognized among the scientific community that high frequencies of the gene reflect its benefit to heterozygotes against malaria. Textbooks normally develop this concept with reference to the often-used maps of Africa showing how in areas where the frequency of the sickle-cell gene is high, there is also higher exposure to the disease malaria. While sickle-cell anemia is often the example of choice for explaining and illustrating the concept of heterozygote protection, the present paper argues that exploring the history of scientific research behind our contemporary understanding has advantages for helping students understand multiple factors related to population genetics (e.g. mutation, gene flow, drift) in addition to heterozygote protection. In so doing, this approach invites students to evaluate the legitimacy of their own alternative conceptions about introductory population genetics or about the genetics of the disease sickle-cell anemia. The various historical theories scientists proposed and defended often resemble those of students who first learn about the disease. As such, a discussion of how scientists reached consensus about the role of heterozygote protection may help students understand and appreciate what are now recognized to be limitations in the views they bring to their classrooms. The paper concludes by discussing the ramifications of this approach in potentially helping students to examine certain aspects of the nature of science.

An explicit and reflective approach to the use of history to promote understanding of the nature of science

“…The authors refer to this as an ''implicit'' approach to learning about the nature of science, by which they mean that students on this model learn about nature of science issues by reflecting on deeply contextualized examples of scientific work. 1 An alternative position (Howe 2004(Howe , 2007Howe and Rudge 2005;Rudge 2004; Rudge and Howe 2004), drawing from the work of Allchin (1993Allchin ( , 2000, is that history of science can and should be used to place students in an epistemological position that invites them to engage in the sort of reasoning used by past scientists to achieve their insights. The basic idea is that students will learn more about the process of science and more about nature of science issues when they are invited to reason as past scientists did, in the absence of knowing what the right answer is or being told about the reasoning of others.…”

The Importance of Attitudes toward and Understanding of Disability and Science in the Age of Genetics

“…Most biological impairments involve both multiple genes and complex interactions with various environmental factors (Hubbard & Wald, 1999). We also know that some genes may cause disease or impairment in one form (e.g., different alleles) but provide a benefit in another formVsuch as malaria protection for persons with the heterozygous form of the gene for sickle cell anemia (Howe, 2005). The list goes on and many of the assumptions and arguments of eugenics proponents have been put to rest by sound scientific methodologies.…”