No abstract

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.

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.

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.

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.

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 Ͼ600 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.

By using fluorescent antibody staining, we have followed cytoplasmic granules unique to germ-line cells throughout the life cycle of Caenorhabditis elegans. These elements, designated P granules, are segregated exclusively to germ-line precursor cells during early embryogenesis. Prior to mitosis at each ofthe early cleavages that produce a somatic and germ-line daughter cell, the granules become localized in the region of cytoplasm destined for the germ-line daughter. After the 16-cell stage, the granules appear to be associated with the nuclear envelope. P granules persist in the germ cells throughout the larval and adult stages. The P granules are similar in number, size, and distribution to germ-line-specific structures identified as "germinal plasm" by electron microscopy in C. elegans embryos.Asymmetric segregation ofcytoplasmic components is observed during the early cleavages of many invertebrate embryos (1 (4) or by digesting adult worms with 1% NaOCl in 0.5 M NaOH (5). The embryos were transferred to a drop of M9 salt solution on a polylysine-coated slide (6), covered with a silanized coverslip, made permeable by freezing the slide on dry ice and then popping off the coverslip, fixed in absolute methanol at 40C for 20 min, and air dried. Larvae were picked from plates and fixed as described for embryos. Adult gonads and gametes were obtained by cutting open adult worms in M9 salt solution on polylysine-coated slides, frozen as described above, fixed in acetone at -200C for 20 min, and air dried. Fixed preparations were incubated with undiluted nonimmune rabbit serum for 1 hr at 250C and then overnight with F-RAM (1:40) in phosphate-buffered saline (150 mM NaCl/3 mM KCV8 mM Na2HPOJ1.5 mM KH2POJ1 mM MgCl2) at 4°C. The slides were washed for 90 min with three changes of the same buffer at 10°C, treated with diamidinophenylindole (DAPI) hydrochloride (0.5 ,ug/ ml; Boehringer-Mannheim) in phosphate-buffered saline, rinsed with H20, and mounted in Gelutol (Monsanto) mounting fluid.Microscopy. A Zeiss photomicroscope equipped with Nomarski and epifluorescence optics was used for observation and photography. Each embryo preparation was first photographed with 440-to 490-nm epi-illumination to visualize the immunofluorescence and then simultaneously with visible transmitted light and 365-nm epi-illumination to visualize the embryo and the DAPI-stained chromosomes. For larval and gonad preparations, the Nomarski, DAPI, and immunofluorescence images were photographed separately. RESULTSCleavage of the fertilized C. elegans egg (P0) includes four successive asymmetric divisions (Fig. 1), each generating a larger somatic precursor cell and a smaller P cell (7). The resultant P4

The distinction between soma and germline was recognized more than a century ago: somatic cells form the body of an organism, whereas germ cells serve to produce future generations. In Caenorhabditis elegans, the separation of some and germline occurs through a series of asymmetrical divisions, in which embryonic germline blastomeres divide unequally to produce one somatic daughter and one germline daughter. Here we show that after each asymmetrical division, embryonically transcribed RNAs are detected in somatic, but not germline, blastomeres. This asymmetry depends on the activity of the germline specific factor, PIE-1. In the absence of PIE-1, embryonically transcribed RNAs are detected in both somatic and germline blastomeres. Furthermore, ectopic expression of PIE-1 in somatic blastomeres can significantly reduce the accumulation of new transcripts in these cells. Taken together, these results suggest that germ-cell fate depends on an inhibitory mechanism that blocks new gene expression in the early embryonic germ lineage.