Abstract:

We have developed a new experimental setup for second year Genetics students of the following university degrees: Biology, Biotechnology, Biochemistry and Biomedical Sciences from the Faculty of Biology (Universitat de Barcelona). The main objective is to perform a genetic analysis of the mutation su (sense ulls = dramatic reduction of eye size) of the model species Drosophila melanogaster.

To do so, students must answer three questions:
1. Discern whether this mutation is dominant or recessive;
2. Determine in which chromosome is the mutation located; and
3. Identify the mutant.

For this purpose, students work in teams of four members, and each one carries out a different genetic cross. The first one performs the genetic cross: ebony su strain x vestigial strain, whereas the second student carries out the reciprocal cross. In the first generation, it will be possible to know if the trait is dominant or recessive, and also if it is autosomal or related to a sex chromosome. Since it is established that ebony and vestigial genes are located in chromosome III and II, respectively, in the second generation it is possible to ascertain the chromosomal location of su mutation. The third team member crosses su individuals with flies from the Del strain, which contains a chromosomal deletion covering the region where su is located. Thus, analyzing the offspring obtained students could deduce approximately the region where su mutant is located. The last student carries out a complementation test, crossing su and su2 flies, which correspond to the well known mutant strain eyegone, which shows an eye reduction phenotype similar to su. The resulting offspring present reduced eyes, indicating that both mutations correspond to the same gene (the previously described eyegone). Finally, since students work in a team, the information provided from each genetic cross is integrated to answer the initial proposed questions. Since in Drosophila melanogaster each generation takes two weeks, and the practical sessions are carried out once per week, in the practical sessions between generation analyses, students learn the use of the FlyBase database.

Through this database, students should:
1. Identify possible candidate genes that would correspond to the su mutation; and
2. Understand the structure of the balancer chromosome that maintains the chromosome carrying the deletion.

In both cases, they use the FlyBase computer database. The integration between laboratory and computer sessions is fundamental and allows reaching an outstanding number of competences, for instance: teamwork, communication and transference of results, use of laboratory material, search for information from databases, scientific language use, carrying out genetic analysis by means of Drosophila crosses, integration of genetic concepts and their application, data analyses, drawing conclusions and discussing the obtained results.

Keywords:

Genetics, Drosophila, mutation, chromosomes, genetic crosses, computer database, integration laboratory-computer.