Problem Based Learning (PBL) makes use of real-life scenarios to stimulate students' prior knowledge and to provide a meaningful context that is also related to the student's future professional work. In this article, Paternity testing is presented using a PBL approach that involves a combination of classroom, laboratory, and out-of-class activities: in relation to a fictitious newborn found on the Campus, students design a PCR based protocol to determine their own genotype for two markers. Pooled class genotypes serve to calculate allelic frequencies and to assess Hardy-Weinberg equilibrium. Individual results are also evaluated for possible paternity. The goals of the activity and how each step in the process relates to learning outcomes are presented. Classroom discussions, group discussions, tutorial sessions, wiki sites, laboratory activities, and individual reports sum up the situations, in which the students' process of learning and learning outcomes can be evaluated.

Students often have an oversimplified view of biological facts, which may hinder subsequent understanding when conceptual complexity gives rise to cognitive conflicts. To avoid this situation here, we present a PBL approach for the analysis of Ehlers-Danlos syndrome (EDS), which integrates a variety of topics in cell biology, genetics, and molecular biology, and it is used to illustrate the inherent complexities in some classical biological concepts. Students of two different courses analyze phenotypic, cellular, and molecular characteristics of EDS. Effect of mutations on collagen synthesis on collagen genes' expression and regulation or on connective tissues is reviewed and discussed. Information retrieval is used to develop students' skills in web-based molecular biology tools. Student interest and motivation is increased with the development of diagnostic protocols for a tissue biopsy and for an EDS causing mutation. Expected learning outcomes after completion of the project are also presented.When teaching biosciences (cell biology, genetics, or molecular biology), sometimes we face with what we have called the ''black-or-white concept'' problem: students tend to have an oversimplified view of biological facts, ignoring possible alternatives. When a student has learnt a basic and simplified concept, for example, the concept of ''allele'' illustrated in Mendel's laws, it is often difficult to introduce new complexity on it, giving rise to cognitive conflicts. Cognitive conflict has been defined as a perceptual state where one notices the discrepancy between one's cognitive structure and environment (external information), or between the components of one's cognitive structure (i.e., one's conceptions, beliefs, sub-structures, and so on) [1]. The dichotomous alternative characters in peas, as are green or yellow cotyledons or wrinkled or smooth seeds, get so fixed in students' notion of allele that cognitive conflict arise when allelic series are presented. The same can be said for genotype-phenotype interactions, gene/s-protein/s relationships, cell structure/function, and so on.We have taught Cell Biology (I.S.) and Human Genetics (A.V.) for more than 20 years, and we have been progressively moving to a problem-based approach [2]. Problem-based Learning (PBL) offers an instructional scenario, where students can rediscover concepts, expand them, and resolve conceptual conflicts otherwise pervasive and resistant to change through traditional expository forms of instruction [3]. At the same time, they engage in critical thinking about, in this case, biological facts [4,5].Our courses have a partial PBL format: although PBL is learner-centred, we have adopted a blended model to guide students towards topics and relations that would not usually emerge from their own research. The scenario presented here is performed by undergraduate students at two different stages, Cell Biology for first course Biology students and Human Genetics for third course Biology students, and we have developed this activity having in m...