Additional green light induces shade response symptoms in Brassica rapa as evidenced by increased lateral root spread.

In some plant species, green light (500 to 570 nm) has been shown to act as a shade signal, which stimulates non-photosynthetic photoreceptors to initiate a response that promotes shading symptoms, including lateral root formation. No studies to date have examined whether green light induces shading symptoms in Brassica rapa specifically. Here, we report increased hypocotyl length, root width, and increased width:depth ratio of root architecture in plants grown under additional green light compared to red and blue light, and white light alone. Results indicate that green light acts as a shade signal in B. rapa to induce shading symptoms, including wider roots.

Biological Variation as a Threshold Concept: Can We Measure Threshold Crossing?

Threshold concepts are fundamental to a discipline and, once understood, transform students' understanding and perception of the subject. Despite the value of threshold concepts as a learning "portal" for heuristic purposes, there is limited empirical evidence of threshold crossing or achieving mastery. As a threshold concept, biological variation within species is fundamental to understanding evolution and provides a target for analyzing threshold crossing. We aimed to 1) examine student understanding of variation using four dimensions of a threshold concept (discursive, troublesome, liminal, and integrative), 2) measure "threshold crossing," and 3) investigate the utility of the threshold concept framework to curriculum design. We conducted semistructured interviews of 29 students affiliated with a "variation-enriched" curriculum in a cross-sectional design with precurriculum, current, and postcurriculum groups (Pre, Current, and Post) and an outgroup of three postbaccalaureate advanced learners (Outgroup). Interview transcripts revealed that Current students expand their "variation discourse," while the Post group and Outgroup displayed conformity in word choice about variation. The Post and Current groups displayed less troublesome and more integrative responses. Pre, Post, and Outgroup explanations' revealed liminality, with discomfort and uncertainty regardless of accuracy. When we combined all four threshold concept dimensions for each respondent, patterns indicative of threshold crossing emerged along with new insight regarding curricular design.

Crossing the Threshold: Bringing Biological Variation to the Foreground.

Threshold concepts have been referred to as "jewels in the curriculum": concepts that are key to competency in a discipline but not taught explicitly. In biology, researchers have proposed the idea of threshold concepts that include such topics as variation, randomness, uncertainty, and scale. In this essay, we explore how the notion of threshold concepts can be used alongside other frameworks meant to guide instructional and curricular decisions, and we examine the proposed threshold concept of variation and how it might influence students' understanding of core concepts in biology focused on genetics and evolution. Using dimensions of scientific inquiry, we outline a schema that may allow students to experience and apply the idea of variation in such a way that it transforms their future understanding and learning of genetics and evolution. We encourage others to consider the idea of threshold concepts alongside the Vision and Change core concepts to provide a lens for targeted instruction and as an integrative bridge between concepts and competencies.

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.

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.

Studying human disease genes in Caenorhabditis elegans: a molecular genetics laboratory project.

Scientists routinely integrate information from various channels to explore topics under study. We designed a 4-wk undergraduate laboratory module that used a multifaceted approach to study a question in molecular genetics. Specifically, students investigated whether Caenorhabditis elegans can be a useful model system for studying genes associated with human disease. In a large-enrollment, sophomore-level laboratory course, groups of three to four students were assigned a gene associated with either breast cancer (brc-1), Wilson disease (cua-1), ovarian dysgenesis (fshr-1), or colon cancer (mlh-1). Students compared observable phenotypes of wild-type C. elegans and C. elegans with a homozygous deletion in the assigned gene. They confirmed the genetic deletion with nested polymerase chain reaction and performed a bioinformatics analysis to predict how the deletion would affect the encoded mRNA and protein. Students also performed RNA interference (RNAi) against their assigned gene and evaluated whether RNAi caused a phenotype similar to that of the genetic deletion. As a capstone activity, students prepared scientific posters in which they presented their data, evaluated whether C. elegans was a useful model system for studying their assigned genes, and proposed future directions. Assessment showed gains in understanding genotype versus phenotype, RNAi, common bioinformatics tools, and the utility of model organisms.

Using online lectures to make time for active learning.

To make time in class for group activities devoted to critical thinking, we integrated a series of short online lectures into the homework assignments of a large, introductory biology course at a research university. The majority of students viewed the online lectures before coming to class and reported that the online lectures helped them to complete the in-class activity and did not increase the amount of time they devoted to the course. In addition, students who viewed the online lecture performed better on clicker questions designed to test lower-order cognitive skills. The in-class activities then gave the students practice analyzing the information in groups and provided the instructor with feedback about the students' understanding of the material. On the basis of the results of this study, we support creating hybrid course models that allow students to learn the fundamental information outside of class time, thereby creating time during the class period to be dedicated toward the conceptual understanding of the material.

Aligning goals, assessments, and activities: an approach to teaching PCR and gel electrophoresis.

Polymerase chain reaction (PCR) and gel electrophoresis have become common techniques used in undergraduate molecular and cell biology labs. Although students enjoy learning these techniques, they often cannot fully comprehend and analyze the outcomes of their experiments because of a disconnect between concepts taught in lecture and experiments done in lab. Here we report the development and implementation of novel exercises that integrate the biological concepts of DNA structure and replication with the techniques of PCR and gel electrophoresis. Learning goals were defined based on concepts taught throughout the cell biology lab course and learning objectives specific to the PCR and gel electrophoresis lab. Exercises developed to promote critical thinking and target the underlying concepts of PCR, primer design, gel analysis, and troubleshooting were incorporated into an existing lab unit based on the detection of genetically modified organisms. Evaluative assessments for each exercise were aligned with the learning goals and used to measure student learning achievements. Our analysis found that the exercises were effective in enhancing student understanding of these concepts as shown by student performance across all learning goals. The new materials were particularly helpful in acquiring relevant knowledge, fostering critical-thinking skills, and uncovering prevalent misconceptions.

Supplementing introductory biology with on-line curriculum*.

We developed web-based modules addressing fundamental concepts of introductory biology delivered through the LON-CAPA course management system. These modules were designed and used to supplement large, lecture-based introductory biology classes. Incorporating educational principles and the strength of web-based instructional technology, choices were made about knowledge presentation, representation, and construction (W. A. Nelson, D. B. Palumbo (1992) J. Educ. Media Hypermedia 1, 287-299). Knowledge presentation focused on big and connecting ideas. Knowledge representation provided students the opportunity to interact with concepts in several ways using multiple representations. For knowledge construction, we facilitated students' active and meaningful interactions with content using interwoven high-level questions. Students' extended responses to a questionnaire indicated that these modules influenced the students learning in meaningful ways. (For access to demonstration modules, go to demo.lon-capa.org/cgi-bin/signon.pl?hhmi.).