Introduction: Genetics


Using Yeast to Teach Genetics

Genetics in the Science Curriculum

The discipline of genetics provides a set of unifying concepts for teaching all aspects of biology. But more than that, it provides a compelling focus for stimulating interest in learning biology. Although some of us are interested in wildlife or plants or aspire to careers in health services, we are all interested in how we got to be as we are, and in what our children will be like. The study of genetics caters to these universal interests, stimulating a desire to understand diverse aspects of biology, chemistry, physics, and mathematics.

Understanding genetics is particularly timely and relevant to many major issues of public concern regarding the role of human heredity and individual variation in health-related issues such as cancer, heart disease, alcoholism, and drug addiction. Environmental mutagens and carcinogens, such as ultraviolet radiation, ionizing radiation from radioactive waste and reactor accidents, food additives, agricultural chemicals, and industrial solvents, are common types of risk-versus-benefit controversies. And the most frightening, and threatening health risk of our time, AIDS, can only be understood and controlled through application of techniques and insights from molecular genetics. Finally, biotechnology, primarily based on molecular genetics, is offering solutions to many serious, and not so serious, problems -- solutions which themselves have the potential of becoming new problems.

In short, a knowledge of genetics is fundamental to understanding biology and essential for understanding many of the most important public issues that we face.

A Paradox: Genetics is Hard Because it is Simple

Genetics has a reputation for being hard to teach and hard to learn. Ironically, this is primarily because genetics is fundamentally simple. But "simple" does not necessarily mean "easy." Genetics is "simple" because it can be reduced to an abstract formalism. General principles can explain many specific observations, and predictions can be made with probabilities that can be calculated. But it has been well established that for most students, even for most college undergraduates, learning abstract principles is hard. The most recent milestone in biology research is the mapping of the nucleotide sequence of the entire yeast genome: 12 million base pairs. The dramatic progress in molecular genetics, in large part because of technical simplicity, can make teaching more effective: We can use simple microorganisms and uncomplicated methods and techniques. Experiencing directly, simply, and quickly the fundamentals of genetics will help students make the connections between simple, concrete observations and abstract generalizations.

A Simple Truth: Science is Research The opinions of some philosophers and science education specialists not withstanding, science is what scientists do and scientists do research. Obviously, the best way for anyone to study science is to do some research. To learn about scientists' current understanding of the universe -- the results of science, which are transient and continuously being updated -- one must read papers and books written by scientists or textbooks and other reference books. But to learn what scientists really do and how they know what they tell us, there is no substitute for doing research. In the case of genetics, doing research requires understanding the biology and traits of a suitable research organism well enough to do experiments on how its genetic material is organized and how it functions.

Using Yeast to Simplify Teaching and Learning Genetics

Yeast offers just about everything we could ask for in an organism suitable for doing genetics. Yeast experiments offer an easy and economical growth, a short generation time, hundreds of interesting mutants, an easily manipulated complete sexual cycle, simple equipment requirements (petri plates and toothpicks), and even a pleasant smell. Baker's Yeast (Saccharomyces cerevisiae) has become the most studied single-cell eukaryotic ("having a nucleus") organism (Roman 1981). Consequently, one can easily demonstrate a wide range of genetic and physiological processes with yeast, including response to environmental factors such as radiations and hazardous chemicals. One result of yeast's unique qualities as a genetic organism is that it was selected as the first eukaryotic organism to have its genome completely mapped. The genetic sequence of the entire yeast genome -- some 12 million base pairs --

is now known and available to researchers through data bases on the Internet. Yeast artificial chromosomes (YAC) are also being used as a central tool for determining the sequence of the human genome. Using this Classroom Guide in the Biology Curriculum: These materials, evolved over the past decade through collaborations among several hundred secondary biology teachers and a group of scientists, informally knows as the Genetics Education Network. These collaborations established that the yeast system described here was useful for creating a research-based approach to the study of genetics and genetic-environmental interactions. We have assembled a variety of materials for both teachers and students to help establish a realistic research environment in the classroom. We have been guided by the following assumptions: 1. Text books have little if any place in the research environment, so this Guide is not intended to be used as a textbook. 2. The knowledge and training of teachers and students in the secondary grade levels varies greatly, as does the amount of time available, so we have provided information at a wide range of detail sophistication. We have not attempted to write to a particular reading level for either students or teachers. 3. Teachers and students will use the materials in many different ways. Some teachers want student-ready handouts, while others will completely rewrite their own. Therefore, we have adopted a loose-leaf format and graduated presentation, so teachers can put together what they need, combining it with other sources, including their own creations. 4. The research literature is not generally available or suitable for most teachers and students, so we have attempted to make the material self-sufficient. 5. A research approach focuses the emphasis on methods and techniques. We have tried to provide enough information and specific examples to permit the development of the basic laboratory techniques for experiment with yeast. Specific techniques are developed by researchers through pains-taking experimentation so we have presented these in specific detailed instructions based on the experience of professional researchers. They reflect the best practices we know, adapted to the limitations of classrooms. 6. Student inquiry is a valuable learning technique. That is, in fact, what we mean when we speak of research. In most cases, however, we have written procedures with the same specific instructions that scientists share with each other in research papers. We like to distinguish between inquiry and guessing. Inquiry is central to the question-asking aspects of research. Applying the best techniques available is central to the question-answering aspect. Format of the Classroom Guide Part A describes yeast as a research organism. It includes the basic life-cycle, genetics, metabolism, and the response of yeast to environmental radiations. The special features of yeast that are used in the experiments are described, with emphasis on the red/white color traits. Many of the topics introduced here are described in greater detail in later sections. Parts B through E contain specific experiments. The format of each experiment is generally as follows: The first page is a brief introduction and description, intended for both students and teachers. The following even-numbered pages (two-column format) contain specific experimental procedures, including a time line and required materials. These can be used directly as student handouts, or modified by the teacher. The facing odd-numbered pages (single-column format), labeled "Teacher-Tips", are specific notes keyed to the experimental procedures to support the classroom logistics. These notes are written primarily by teachers who have used the materials in their classroom. The odd/even organization makes it easy to photocopy the experimental procedures without the "Teacher-Tips." Part F presents a series of essays, called "A Closer Look.." to provide more detailed information about major topics for teachers and more capable students. These are written by research scientists to fill the gap between nonexistent or superficial textbook treatments of the topics and the generally inaccessible research literature. Part G is a reference guide to the standard laboratory techniques required for these experiments. While it is written with yeast in mind, many of the microbiological techniques described are useful for bacteria as well. We have modified these techniques, where necessary, to make them safe, simple, and inexpensive. For example, we have eliminated the use of flames in nearly all microbiological procedures, and the use of Baker's yeast itself eliminates the risk of potentially infections microorganisms. Part H complete annotated scripts for the video tape segments of the accompanying video tapes. These tapes illustrate many of the experiments and techniques, show examples of expected results, and provide supplementary graphical materials. Part I contains a glossary of technical terms used in the Guide. The scientists and teachers writing the experiments wrote these definitions to convey their intended meaning of the terms in the context of the experiments. Also, there is a lists references to the research literature cited in the experiments and some review articles considered appropriate.

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Last updated Friday July 11 1997