Difficulties in Genetics Problem Solving

Richard R. Tolman is a Staff Associate at the Biological Sciences Curriculum Study, 833 W. South Boulder Road, Louisville, CO 80027, and Adjunct Associate Professor, School of Education, University of Colorado, Boulder. He received his B.S. and M.S.Ed. degrees from the University of Utah and the Ph.D. degree from Oregon State University. He has taught junior high general science and health at South Davis Junior High School and general biology at Mount Hood Community College, Gresham, Oregon. He has been a member of the BSCS staff since 1969. The Center for Educational Research and Evaluation received an NSF grant under the Research in Science Education (RISE) program to conduct an expert-novice study of problem solving in genetics. Three different types of genetics problems were used in the study-a monohybrid cross, a codominance problem, and a problem with sex-linked inheritance. High school students were asked to solve these problems in a think-outloud mode. Each problem-solving session was recorded on audio tape. Thirty junior or senior students in one Colorado high school who had previously completed a sophomore-level biology course were the subjects of the study. While analyzing the typed transcripts of the problem-solving sessions, and the worksheets used by the students, some common patterns began to emerge. Although these common patterns did not relate specifically to the goals of the study, they did provide insight into problem-solving methodology and seemed important and worthy of reporting. It should be noted that this is not an attempt to generalize conclusions to the population of high school biology students. The results apply only to the group within this study. However, correspondence with colleagues at the University of Wisconsin and at West Virginia University indicate that students' problem solving in genetics at those institutions is yielding similar results. One of the major difficulties encountered by the 30 students was understanding the concept that the pairs of alleles in an offspring are the result of transmission of one allele from each of the parents of the offspring. More specifically, the students experience difficulty in associating the alleles with chromosomes and chromosome behavior and the segregation and random assortment during the first division of meiosis. While constructing Punnett squares, students would commonly assign two alleles to each parent for an F1 trait. This error was manifested in the production of a Punnett square similar to that in figure 1. This resulted in offspring with four alleles for each trait. Only 6 of 30 students (20%) accurately described the parental source of each allele in a pair of alleles for normal vision (M) and myopia (m).