yeast genetics
Yeast genetics uses single-celled fungi — most often baker's yeast, Saccharomyces cerevisiae — as a model for how the cells of complex organisms, including ours, actually work. A yeast cell is a eukaryote, meaning its DNA is packaged in a nucleus like our own, yet it grows as fast and as cheaply as bacteria, so questions about eukaryotic cells can be answered in days rather than months.
Yeast can live and divide as either a single-copy (haploid) or double-copy (diploid) cell, and it can be made to mate or to reproduce by budding, which gives geneticists exquisite control over crosses and mutations. Its compact genome was among the first fully sequenced, and ordered collections exist in which each gene has been deleted one at a time, allowing the function of nearly every gene to be probed systematically.
Despite being a humble microbe, yeast shares the core machinery of eukaryotic life — how DNA is copied, how the cell cycle is controlled, how proteins are sorted and how genes are switched on. Many such processes were first understood in yeast and later found to operate, often through closely related genes, in human cells.
The genes that control when a cell divides — the cell-cycle checkpoints — were first mapped in yeast, and the same control system, with related genes, governs division in human cells.
A microbe that taught us how our own cells divide.
Because human and yeast genes are often interchangeable, a broken yeast gene can sometimes be rescued by inserting its human counterpart — a quick test of whether the two genes do the same job.