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What is aneuploidy?

yeast cell To reproduce themselves accurately, cells must do two things: (1) make a copy of all their DNA (replication) and (2) evenly separate each copy into the new daughter cells (mitosis). Cells can do this with remarkable accuracy.

However, mistakes do happen. Yeast cells, for example, fail to separate chromosome copies once every 10,000-1,000,000 cell divisions. When this happens, each daughter cell obtains a different set of chromosomes than the parent cell: one daughter will be missing a chromosome and the other daughter will have mistakenly received that chromosome, making it an extra one. This chromosomal state is called aneuploidy.

yeast cellAneuploidy can affect the health or the "phenotype" of cells and organisms. Down syndrome, for example, results when a child receives one extra chromosome. But in some environments, the effects of aneuploidy might give cells particular growth advantages. For instance, cancer cells that can outgrow their neighbors frequently have aberrant numbers of chromosomes. Yeast cells grown many generations in a laboratory can sometimes become aneuploid or exhibit chromosome rearrangements.

Are aneuploidies related to growth advantages in these cases? Or are they byproducts of some other problem in the cell? How exactly does an extra chromosome affect a cell? These are the kinds of questions we want to answer. To do so, we are engineering strains of yeast where the only difference between them will be the presence of an extra chromosome. We are studying these strains to characterize and document how they differ from normal yeast cells.