ABSTRACT
The primary goal of this project was to assess long-term retention of concepts and critical thinking skills in individuals who completed a Developmental Biology course. Undergraduates who had completed the course between 2006 and 2009 were recently contacted and asked to complete a professional goals survey and a multiple-choice developmental biology assessment test (DBAT) targeting four levels of learning. The DBAT was designed to assess students' retention of knowledge and skills related to factual recall, concept application, data analysis, and experimental design. Performance of the 2006-2009 cohorts was compared to that of students enrolled in 2010 who completed the DBAT at the beginning and the end of the semester. Participants from the 2010 course showed significant learning gains based on pre- and posttest scores overall and for each of the four levels of learning. No significant difference in overall performance was observed for students grouped by year from 2006-2010. Participants from the 2006-2009 cohorts scored slightly, but significantly, higher on average if they enrolled in graduate or professional training. However, performance on individual question categories revealed no significant differences between those participants with and without postundergraduate training. Scores on exams and a primary literature critique assignment were correlated with DBAT scores and thus represent predictors of long-term retention of developmental biology knowledge and skills.
ABSTRACT
Seed plant female gametophytes are focal points for the evolutionary modification of development. From a structural perspective, the most divergent female gametophytes among all seed plants are found in Gnetum, a clade within Gnetales. Coenocytic organization at sexual maturity, absence of defined egg cells (free nuclei are fertilized), lack of centripetal cellularization, and postfertilization development of embryo-nourishing tissues are features of the female gametophytes of Gnetum unparalleled among seed plants. Although the female gametophyte of Gnetum retains the three basic phases of somatic development common to female gametophytes of plesiomorphic seed plants (free nuclear development, cellularization, cellular growth), the timing of fertilization has been accelerated relative to the rate of somatic development. As a consequence, the female gametophyte of Gnetum matures sexually (is fertilized) at a juvenile (compared with the ancestral somatic ontogeny) and free nuclear stage of somatic development, thereby precluding differentiation of egg cells. Unlike progenetic animals, where truncation of somatic ontogeny evolves in tandem with acceleration in the timing of sexual maturation, the female gametophyte of Gnetum completes the entire ancestral somatic ontogeny after precocious sexual maturation. This results in the evolution of postfertilization development of embryo-nourishing female gametophyte tissues, a phenomenon unique among seed plants. Nonheterochronic developmental innovations have also played important roles in the evolution of the female gametophyte of Gnetum. Centripetal cellularization, which is always associated with the phase change from coenocytic to cellular organization among plesiomorphic seed plant female gametophytes, is lacking in Gnetum. Instead, during early phases of development, apomorphic free nuclear organization is coupled with a highly anomalous pattern of cellularization. Stage-specific innovations during early development in the female gametophyte of Gnetum do not affect plesiomorphic aspects of later phases of development. Thus, a complex array of heterochronic and nonheterochronic developmental innovations have played critical roles in the ontogenetic evolution of the highly apomorphic female gametophyte of Gnetum.
