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( Mating of yeast)
The yeast Saccharomyces cerevisiae is a simple single celled eukaryote with both a diploid and haploid mode of existence. The mating of yeast only occurs between haploids, which can be either the a or a (alpha) mating type and thus display simple sexual differentiation. Mating type is determined by a single locus, MAT, which in turn governs the sexual behaviour of both haploid and diploid cells. Through a form of genetic recombination, haploid yeast can switch mating type as often as every cell cycle. These phenotypic differences between a and a cells are due to a different set of genes being actively transcribed and repressed in cells of the two mating types. a cells activate genes which produce a-factor and produce a cell surface receptor (Ste2) which binds to a-factor and triggers signalling within the cell. a cells also repress the genes associated with being an a cell. Similarly, a cells activate genes which produce a-factor and produce a cell surface receptor (Ste3) which binds and responds to a-factor, and a cells repress the genes associated with being an a cell. The different sets of transcriptional repression and activation which characterize a and a cells are caused by the presence of one of two alleles of a locus called MAT MATa or MATa. The MATa allele of MAT encodes a pair of genes called a1 and a2, which in haploids direct the transcription of the a-specific transcriptional program (such as expressing STE2 and repressing STE3) which defines an a cell. The MATa allele of MAT encodes the a1 and a2 genes, which in haploids direct the transcription of the a-specific transcriptional program (such as expressing STE3, repressing STE2) which causes the cell to be an a cell. Like the differences between haploid a and a cells, different patterns of gene repression and activation are responsible for the phenotypic differences between haploid and diploid cells. In addition to the specific a and a transcriptional patterns, haploid cells of both mating types share a haploid transcriptional pattern which activates haploid-specific genes (such as HO) and represses diploid-specific genes (such as IME1). Similarly, diploid cells activate diploid-specific genes and repress haploid-specific genes.
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Estimating The True Total Cost Of Gastric Bypass Surgery by Donald Saunders
Gastric bypass surgery can be expensive and one problem for many people is that they embark on this particular road knowing the baseline cost but overlook the fact that for a whole variety of reasons, often outside of their control, the true total co...
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