Beyond Punnett squares: Student word association and explanations of phenotypic variation through an integrative quantitative genetics unit investigating anthocyanin inheritance and expression in Brassica rapa Fast plants

Abstract

Genetics instruction in introductory biology is often confined to Mendelian genetics and avoids the complexities of variation in quantitative traits. Given the driving question "What determines variation in phenotype (Pv)? (Pv=Genotypic variation Gv + environmental variation Ev)," we developed a 4-wk unit for an inquiry-based laboratory course focused on the inheritance and expression of a quantitative trait in varying environments. We utilized Brassica rapa Fast Plants as a model organism to study variation in the phenotype anthocyanin pigment intensity. As an initial curriculum assessment, we used free word association to examine students' cognitive structures before and after the unit and explanations in students' final research posters with particular focus on variation (Pv = Gv + Ev). Comparison of pre- and postunit word frequency revealed a shift in words and a pattern of co-occurring concepts indicative of change in cognitive structure, with particular focus on "variation" as a proposed threshold concept and primary goal for students' explanations. Given review of 53 posters, we found ∼50% of students capable of intermediate to high-level explanations combining both Gv and Ev influence on expression of anthocyanin intensity (Pv). While far from "plug and play," this conceptually rich, inquiry-based unit holds promise for effective integration of quantitative and Mendelian genetics.

Figure 1.

Aggregate word frequency change from preunit to postunit word association task given the stimulus word “genetics” in 2011 and 2012. Lines connect identical words as they appear in 2011 and 2012, with orange lines indicating positive change in both years, black lines indicating a negative change in both years, and dashed lines indicating a switch between years. (Pre- and postunit: n = 98 and 95 in 2011; n = 95 and 102 in 2012.)

Figure 2.

Word matrices for 2011 pre- and postunit survey of student five-word cluster word associations representing words that occurred in at least 20 student responses across both years (see Supplemental Material 7 for 2012 matrices). Each red shaded cell on the diagonal represents individual word occurrence or relative frequency. Each blue cell colorimetrically represents paired word co-occurrence (dark blue for high co-occurrence, light blue for low co-occurrence). All cell scores were standardized by total student respondents and were relativized to a scale of zero to one (high relatedness) by dividing all cells by the maximum standardized frequency of occurrence or co-occurrence across years and pre/postunit groups. (A) Preunit occurrence and co-occurrences (n = 98); (B) postunit occurrence and co-occurrences (n = 95).

Figure 3.

Self-reported student understanding of genetics terms on the pre- and postunit survey (n = 98 and 95). Data reported here include the percent of students reporting advanced understanding (working knowledge or deep-level understanding), introductory to intermediate understanding, or never heard/don't understand.

Figure 4.

Percent of students’ explanations on the influence of genotypic variation (Gv) and environmental variation (Ev) at each rubric level (missing, low, intermediate, and high) through analysis of final research posters (n = 53).