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Many of the same features of the yeast Saccharomyces cerevisiae that have made it so useful as a genetics and molecular biology research organism make it equally useful as a teaching organism. Furthermore, the fact that it is a modern research organism makes it all the more exciting to students and teachers. The unique characteristic of yeast as a unicellular, eukaryotic organism with a complete sexual life cycle is ideal for teaching. A simple monohybrid cross to explore dominance and recessiveness, a dihybrid cross to demonstrate independent assortment, pigmented adenine auxotrophs for investigating the fundamentals of gene action, and easily measured responses to ultraviolet radiation provide an array of appropriate laboratory tools that put real science in the hands of students and teachers. Direct collaborations between scientists and science teachers bring together complementing knowledge and experience, providing an effective and efficient way to adapt and simplify techniques and procedures to accommodate time and money constraints. Collaborations quickly identify technical and theoretical problems that must be solved for implementation in classrooms. They also provide a continuing stimulus to teachers and students to participate in the research process.

HE actions of genes controlling quantitative characters may be described the use of gene models. FISHER (1918) constructed a gene model which included dominance at a single locus. He stated that there may be a deviation from the simple additive effects between loci, similar to dominance at one locus, if more than one locus affected a given character. He called the deviation epistacy and introduced the term dual epistacy to indicate the interaction of all possible pairs of loci affecting the given character. Later, FISHER, IMMER and TEDIN (1932) used this gene model to describe the actions of any number of genes on a given character assuming there was no epistacy. GRIFFING (1950) introduced an epistatic parameter into a model, but the model is not easily extended to an arbitrary number of loci. The present paper contains a model based on the factorial model used in the design of experiments and some applications of this model to some data. THE FACTORIAL GENE MODEL The factorial model may be exemplified by the case of a dihybrid. The relative frequencies of the nine genotypes obtained from selfing the complete heterozygote may be represented in the following manner