A global analysis of ploidy maintenance in S. cerevisiae

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In cells the genetic material (DNA) is stored in complex structures called chromosomes. Every organism has a specific number of chromosomes, and this is constant in all cells in the organism (with some exceptions, such as germ cells-for example, eggs and sperm in humans). It is essential for the proper function of a cell that it contains a complete copy of the DNA, packaged into the correct number of chromosomes. Unfortunately, this poses a problem for cells when one cell grows and divides to form two cells: How to make sure that both daughter cells have the correct number of chromosomes? To accomplish this feat, cells first copy all of their DNA so that they contain two of each chromosome, and then the chromosomes are divided accurately between the daughter cells. We are studying how the correct number of chromosomes is maintained as cells grow and divide, in the simple single-cell organism Saccharomyces cerevisiae (baker's yeast). The simplicity of this organism, relative to more complicated ones like plants or animal, makes it a good system for figuring out biological problems, since its systems are typically more compact and streamlined (they have fewer "parts"). Despite this simplicity, similar versions of important biological systems are conserved during evolution, and so are typically present in all organisms, from the simplest to the most complex. Understanding the biology behind fundamental processes like the constant number of chromosomes in a simple organism can then be applied to understanding the same process in, for example, plants and multicellular animals. Our study has the potential to identify all of the systems in yeast that contribute to maintaining a constant and accurate chromosome number. This will be the first time such a complete description of the process has been furnished, and will be of use to scientists studying cell growth and division, and those interested in how differences in chromosome number can affect cellular function.