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Yeast Home
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Research Based Labs with Yeast
Yeast Life Cycle and Basic Genetics
Radiation Effects on
Yeast
Red and White Yeast: An Introduction to Science as a
Process
Transformation of
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Research Based Labs with Yeast
The yeast Saccharomyces cerevisiae is particularly well suited
for exploration of the principles of basic genetics because
it has a complete sexual cycle and numerous nutritional mutations that
serve as markers, allowing segregation of traits to be readily followed in
crosses. A
brief review of the yeast life cycle follows below.
Another area offering the potential for extensive investigation
is the behavior of
yeast when irradiated or treated with other DNA damaging agents;
experiments include basic radiation biology and genetics of radiation
damage repair.
Yeast is also readily transformed with plasmids and chromosomal DNA
fragments and this method of genetic manipulation lends itself to a number
of studies.
Yeast Life Cycle
Saccharomyces cerevisiae is a unicellular fungus that grows on
simple nutritional media. The first strains cultivated were cultured
from grape skins. Yeast can grow vegetatively as either haploids or
diploids and both phases are stable but it is also easy to manipulate
haploids to form diploids and vice versa. There are two sexes, or
mating types, a and  (alpha). These are
controlled by alleles of a single genetic locus, MAT, the
mating type locus. Mixing together a and strains stimulates them to secrete pheromones that cause
the
cells of opposite mating type to form
elongated projections that then allow fusion of a and to form a/ diploids.
Such diploids will then grow vegetatively unless starved for nitrogen. In
this instance, they will initiate the process of meiosis, followed by
spore formation. The four haploid cells resulting from each meiosis
are spores and are encased in a sac called the ascus. This packaging
of the products of individual meioses is what has made yeast and other
ascomycetes (ascus-forming fungi) such valuable organisms for genetic
research. Two of the spores in each ascus will give rise to a
cells and two to cells when they are placed on
nutritionally adequate medium. These are the source of new haploid
strains of yeast. The yeast cell division cycle has been the subject
of intense investigation and is very similar to that of higher
eukaryotes. For more detailed information about the yeast life cycle
see Baker's Yeast and
Its Life Cycle at the GENE web site.
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