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Diana Downs: ENCOURAGING STUDENTS TO THINK RATHER THAN MEMORIZE

One of the challenges I find in teaching is to convince students they need the ability to incorporate facts in solving problems. The idea of problem solving seems to be foreign to many students, who are prone to assume that memorization of facts will suffice. This expectation has been propagated throughout their education, making it difficult to reverse late in their college career. In my mind it is a problem that educators must face, even in elementary school. Information is widely available with the internet and mass media. There are simply endless facts to learn. Thus it is critical that we teach student to problem solve. This is a skill that will stay with them long after their coursework is over. Given good thinking skills students can learn to reconstruct important concepts for themselves when needed, long after facts have been forgotten.

My strategy to improve problem solving skills in the course I teach has been to minimize facts and encourage thinking. I teach an optimal course to do this in; Bacterial Genetics. This is a course taught to primarily juniors, currently about 100/semester. Unfortunately this is not the optimal number to teach problem solving to, since it should involve a lot of discussion and explanation.

Genetics is by nature a deductive science, since in the classical sense we are dealing largely with abstractions. I teach this course as very problem oriented, all exams are exclusively problem based. I provide a large number of practice problems throughout the semester. In general I do not go through problems in my lectures but rather emphasize basic concepts and thought processes. The discussion sections and office hours are to provide help in problem solving. This is a constant source of consternation to the students who assume that if problems are on the exams, I will work problems in class. I emphasize that I am trying to get them to take what they hear in class, understand it to the extent that they can incorporate it into a "real life" situation to solve a problem. This is difficult for many and unfortunately a large number of students feel put out at having to scratch their heads and figure things out without being given the answer.

In general, my point gets across and the students as a whole realize and accomplish my goal. They are proud of their reasoning by the end of the course and many a student has correctly concluded that although the course is called Genetics, it is a course in logic.

Questions for discussion:

Sample Problem (answers are in bold-faced text):

Approximately 108 cells of an unknown mutant bacterial strain are spread on each of a number of plates. The plates were incubated 24 hr at the indicated temperature and the following growth resulted.

medium in plate ( temperature) 40o ( temperature) 30o
minimal no growth 60 colonies
minimal + leucine 10 colonies confluent growth
nutrient (rich) medium 10 colonies confluent growth

a) Suggest a reasonable genotype for this strain.

THERE ARE TWO MUTATIONS IN THE STRAIN.

b) Describe the effect each mutation from a) has on growth of the strain.

LEU- MUTATION PREVENTS THE CELL FROM MAKING LEUCINE AT ALL TEMPERATURES, POSSIBLY DEFECTIVE IN A BIOSYNTHETIC ENZYME TS MUTATION IS IN AN UNDEFINED LOCUS THAT IS ESSENTIAL FOR GROWTH, THE MUTATION IS LIKELY ALTERING THE RESPECTIVE PROTEIN SUCH THAT IT FUNCTIONS AT LEAST MARGINALYY AT LOW TEMPERATURES BUT IS COMPLETELY INACTIVE (OR UNSTABLE) AT HIGH TEMPERATURES.

c) Describe a simply testable prediction of your prediction from a).

IF THE ABOVE GENOTYPE IS CORRECT, THE COLONIES THAT ARISE AT 40 DEGREES WILL STILL BE LEU-. THE COLONIES THAT ARISE AT 30 DEGREES ARE LEU+ BUT WILL STILL BE DEAD AT 40. THERE ARE NO COLONIES AT 40 DEGREES ON MINIMAL MEDIUM BECAUSE THAT WOULD REQUIRE THE REVERSION OF BOTH MUTATIONS, AN EVENT TOO RARE TO DETECT WITH 10(8) CELLS.

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UW-Madison, October 1998 (modified 3/99)