William B. Wood

Teaching more by lecturing less.

We carried out an experiment to determine whether student learning gains in a large, traditionally taught, upper-division lecture course in developmental biology could be increased by partially changing to a more interactive classroom format. In two successive semesters, we presented the same course syllabus using different teaching styles: in fall 2003, the traditional lecture format; and in spring 2004, decreased lecturing and addition of student participation and cooperative problem solving during class time, including frequent in-class assessment of understanding. We used performance on pretests and posttests, and on homework problems to estimate and compare student learning gains between the two semesters. Our results indicated significantly higher learning gains and better conceptual understanding in the more interactive course. To assess reproducibility of these effects, we repeated the interactive course in spring 2005 with similar results. Our findings parallel results of similar teaching-style comparisons made in other disciplines. On the basis of this evidence, we propose a general model for teaching large biology courses that incorporates interactive engagement and cooperative work in place of some lecturing, while retaining course content by demanding greater student responsibility for learning outside of class.

Why Peer Discussion Improves Student Performance on In-Class Concept Questions

When students answer an in-class conceptual question individually using clickers, discuss it with their neighbors, and then revote on the same question, the percentage of correct answers typically increases. This outcome could result from gains in understanding during discussion, or simply from peer influence of knowledgeable students on their neighbors. To distinguish between these alternatives in an undergraduate genetics course, we followed the above exercise with a second, similar (isomorphic) question on the same concept that students answered individually. Our results indicate that peer discussion enhances understanding, even when none of the students in a discussion group originally knows the correct answer.

Generation of asymmetry and segregation of germ-line granules in early C. elegans embryos

Germ-line granules in C. elegans embryos (P granules) can be visualized by immunofluorescence microscopy using a monoclonal antibody. In mutant zygotes with abnormal spindle orientations and in wild-type zygotes treated with the microtubule inhibitors nocodazole, colcemid, vinblastine, and griseofulvin, both P-granule segregation to the posterior pole and the concomitant pseudocleavage occur apparently normally, but the normally concurrent migration of the pronuclei is inhibited. Conversely, treatment of wild-type embryos with the microfilament inhibitors cytochalasins D and B inhibits P-granule segregation and pseudocleavage, as well as other manifestations of polarity, without preventing pronuclear migration. The results suggest that P-granule segregation does not require either the spindle or cytoplasmic microtubules, but that this process as well as generation of other asymmetries does require cytoskeletal functions that depend on microfilaments.

PGL-1, a Predicted RNA-Binding Component of Germ Granules, Is Essential for Fertility in C. elegans

Germ cells are distinct from somatic cells in their immortality, totipotency, and ability to undergo meiosis. Candidates for components that guide the unique germline program are the distinctive granules observed in germ cells of many species. We show that a component of germ granules is essential for fertility in C. elegans and that its primary function is in germline proliferation. This role has been revealed by molecular and genetic analyses of pgl-1. PGL-1 is a predicted RNA-binding protein that is present on germ granules at all stages of development. Elimination of PGL-1 results in defective germ granules and sterility. Interestingly, PGL-1 function is required for fertility only at elevated temperatures, suggesting that germline development is inherently sensitive to temperature.

Segregation of developmental potential in early embryos of Caenorhabditis elegans.

We have followed the appearance of differentiation markers in cleavage-inhibited and uninhibited early blastomeres of C. elegans and have compared the cleavage patterns of blastomeres in partial and complete embryos. The results indicate that at least some primary differentiation of embryonic cells is determined by internal factors that segregate in early cleavages, whereas patterns of cleavage are dictated by both internally segregating determinants and external cues.

The Genetics Concept Assessment: A New Concept Inventory for Gauging Student Understanding of Genetics

We have designed, developed, and validated a 25-question Genetics Concept Assessment (GCA) to test achievement of nine broad learning goals in majors and nonmajors undergraduate genetics courses. Written in everyday language with minimal jargon, the GCA is intended for use as a pre- and posttest to measure student learning gains. The assessment was reviewed by genetics experts, validated by student interviews, and taken by >600 students at three institutions. Normalized learning gains on the GCA were positively correlated with averaged exam scores, suggesting that the GCA measures understanding of topics relevant to instructors. Statistical analysis of our results shows that differences in the item difficulty and item discrimination index values between different questions on pre- and posttests can be used to distinguish between concepts that are well or poorly learned during a course.

Parental effects and phenotypic characterization of mutations that affect early development in Caenorhabditis elegans.

Abstract Genetic tests for parental effects were performed on 24 temperature-sensitive embryonic-lethal mutants of the nematode Caenorhabditis elegans. For 21 of these mutants, maternal expression of the wild-type allele is sufficient for embryonic survival, regardless of the embryos genotype. For 11 of these 21 mutants, maternal expression of the wild-type allele is necessary for embryonic survival (strict maternals). For the remaining 10, either maternal or embryonic expression is sufficient for survival (partial maternals). One mutant shows a paternal effect; that is, a wild-type extragenic sperm function appears to rescue homozygous mutant embryos. Similar parental-effect tests were performed on 11 larval-lethal mutants. In 4 mutants, 1 of which blocks as late as the second larval stage after hatching, maternal contributions still can rescue mutant larvae. The remaining 3 embryonic lethals and 8 larval lethals show no parental effects; that is, zygotic expression of the wild-type allele is necessary and sufficient for embryonic survival. Temperatureshift experiments on embryonic-lethal embryos showed that all but 1 of the strict maternal mutants are temperature sensitive only before gastrulation. One of the partial maternal mutants is temperature sensitive prior to gastrulation, suggesting that some zygotic genes can function early in embryogenesis. At the nonpermissive temperature, 7 of the strict maternal mutants either show cleavage abnormalities in early divisions or stop cleavage at less than 100 cells, or both.

Combining Peer Discussion with Instructor Explanation Increases Student Learning from In-Class Concept Questions

Use of in-class concept questions with clickers can transform an instructor-centered “transmissionist” environment to a more learner-centered constructivist classroom. To compare the effectiveness of three different approaches using clickers, pairs of similar questions were used to monitor student understanding in majors’ and nonmajors’ genetics courses. After answering the first question individually, students participated in peer discussion only, listened to an instructor explanation only, or engaged in peer discussion followed by instructor explanation, before answering a second question individually. Our results show that the combination of peer discussion followed by instructor explanation improved average student performance substantially when compared with either alone. When gains in learning were analyzed for three ability groups of students (weak, medium, and strong, based on overall clicker performance), all groups benefited most from the combination approach, suggesting that peer discussion and instructor explanation are synergistic in helping students. However, this analysis also revealed that, for the nonmajors, the gains of weak performers using the combination approach were only slightly better than their gains using instructor explanation alone. In contrast, the strong performers in both courses were not helped by the instructor-only approach, emphasizing the importance of peer discussion, even among top-performing students.

A Caenorhabditis elegans TGF‐β, DBL‐1, controls the expression of LON‐1, a PR‐related protein, that regulates polyploidization and body length

Using cDNA‐based array analysis combined with double‐stranded RNA interference (dsRNAi), we have identified yk298h6 as a target gene of Caenorhabditis elegans TGF‐β signaling. Worms overexpressing dbl‐1, a TGF‐β ligand, are 16% longer than wild type. Array analysis shows yk298h6 to be one of several genes suppressed in such worms. Disruption of yk298h6 function by dsRNAi also resulted in long worms, suggesting that it is a negative regulator of body length. yk298h6 was then mapped to, and shown to be identical to, lon‐1, a known gene that affects body length. lon‐1 encodes a 312 amino acid protein with a motif sequence that is conserved from plants to humans. Expression studies confirm that LON‐1 is repressed by DBL‐1, suggesting that LON‐1 is a novel downstream component of the C.elegans TGF‐β growth regulation pathway. Consistent with this, LON‐1 is expressed mainly in the larval and adult hypodermis and has dose‐dependent effects on body length associated with changes in hypodermal ploidy, but not hypodermal cell proliferation.

Two loci required for cytoplasmic organization in early embryos of Caenorhabditis elegans

We have identified five new alleles, including an amber allele, at each of two loci (zyg-11 II and zyg-9 II) previously identified by temperature-sensitive strict maternal-effect lethal mutations. Genetic analysis indicates that each of these genes is expressed specifically during oogenesis and encodes a protein product whose function is required only during embryogenesis. Temperature-pulse experiments suggest that the time of action of both products is during the one-cell stage of embryogenesis. Phenotypic analysis reveals that mutations in both loci lead to disorganization of the cytoplasm in early embryos and to abnormalities in at least one of the meiotic divisions. Mutations at the zyg-9 locus appear to specifically affect microtubule function in one-cell embryos while zyg-11 mutations affect many cytoplasmic properties.