Tetrad dissection microscope system for genetic analysis

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The "awesome power of yeast genetics" is a phrase commonly used by scientists employing the yeasts Schizosaccharomyces pombe or Saccharomyces cerevisiae as experimental models.  These relatively simple unicellular organisms have long been used in experiments - aimed at better understanding many aspects of cellular physiology and genetics - that would have been difficult or impossible to perform in higher organisms such as humans.  In this way, research in these yeasts have led to tremendous advancements in our knowledge of how cells control their growth and division, and thus have provided a theoretical framework for understanding the genetics of cancer.  One of the main advantages of studying S. pombe or S. cerevisiae is the ease of genetic analysis.  Key to this genetic analysis is a tool referred to as a tetrad dissection microscope.  This instrument, consisting of a normal light microscope together with complementing micro-manipulation tools (joystick, specialized stage, micro-needle), is used to physically separate the four individual "ascospores" derived from the mating of two individual yeast strains.  By mating two strains carrying mutations in different genes, and then analyzing the separated ascospores, it is possible to isolate a strain carrying both mutations and thus to analyze the genetic interactions between them.  Using this same logic it is possible to create strains containing complex combinations of mutations that can be used to study the genetic control of the biological problem under study.  In this particular instance we are interested in using a tetrad dissection microscope to better understand the genetic regulation of "cytokinesis", the last step of the cell cycle in which an individual mother cell cleaves itself into two independent daughters.