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Yeast, especially Saccharomyces cerevisiae, is an ideal organism in which to study genetics. The growth cycle is short, and you can examine both haploid and diploid colonies in action, as both are viable. You can even exmaine the parent haploid strains, diploid strains, and offspring haploid strains simultaneously because of the short life cycle.

Yeast genes are simple, with only a couple of genes carrying any introns at all. The nomenclature of genes is somewhat clear -- you name a gene according to what it does. For example, the HIS genes are involved in the biosynthesis of HIStidine; the MAT genes are MATing type. Capital letters indicate that the gene is in the dominant form (usually the wild-type gene), while lowercase letters indicate that the gene is recessive. Numbers after the gene name sometimes have meaning, such as the LEU2 gene product being the second protein involved in the leucine biosynthesis pathway; sometimes, though, the numbers are arbitrary, such as HIS1, which I believe is the 4th or 7th step in the histidine biosynthesis pathway, but was the first gene of its type discovered.

(Incidentally, the yeast genome has 16 chromosomes, labelled with Roman numerals I-XVI. Sometimes the chromosome number will appear to indicate on which chromosome the gene is located; sometimes it won't.)

Any gene in the genome can be used as a marker for testing segregation of genes through meiosis (called sporulation in budding yeast). Often, a given strain will carry multiple markers to generate variable segregants, which allows us to study the effects of certain genes and their involvement in the biochemical processes of the cell.

Yeast genetics has given researchers some interesting insights into the genetics or other eukaryotes as well. Yeast is somewhat primitive on the scale of evolution, but many of its processes are homologous to those in plants and animals, including humans.

So those are the basics. What a way to start the day.

Another fantastically useful fact about S. cerevisiae genetics is that it's one of the few organisms that have been fully sequenced. That is, all the genes that it has are known. The functions may not be figured out yet, but you don't have to worry about undiscovered genes.

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