Unformatted text preview: ironment at hand. Meiosis reduces the diploid nucleus
to four haploid nuclei, which become encapsulated in four
haploid spores. On the addition of nutrients, the haploid
cells bud and can divide mitotically.
Yeast populations must experience an alternation of
feast and famine to complete the life cycle. Nutrient depletion induces meoisis and sporulation, while the subsequent
availability of nutrients promotes spore germination and
gamete production. The association of haploid and diploid
phases with periodic ﬂuctuations in environmental conditions is common among eukaryotic microorganisms.
Sex in yeast is determined by the mating type locus
(designated as MAT) on chromosome III. As already mentioned, there are two mating types: a and a. Mating ability
segregates 2a : 2 in tetrads derived from MATa/MAT
heterozygous diploids, indicating that the a and a mating
types are speciﬁed by alleles of a single locus (MAT).
MATa or MAT cells mate efﬁciently with cells of the opposite sex. Heterozygous MATa/MATa diploids are sterile,
but it is possible to derive MATa/MATa o...
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- Spring '08
- DNA, MAT locus, Yeast Geneticist