Chapter 31 : Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment

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Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment, Page 1 of 2

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Saccharomyces cerevisiae is a supermodel organism in the exploding field of genomics. This chapter provides an understanding of the molecular biology by which a genome is converted into phenotypes— the roles played by each gene, mechanisms of gene regulation, responses to stress, the developmental processes of gamete formation, mating, and sporulation, and so on. The mating system of establishes the potential for extensive inbreeding. A haploid yeast individual is one of two mating types, or that mate spontaneously on contact with each other. The signature of recombination is seen in the evolutionary ancestries of different segments of the genome. In an asexual population, the evolutionary histories of all the genes are the same, and phylogenetic trees drawn from different genes are usually the same. Adaptation to organic phosphate limitation in two independent chemostat experiments occurred by chromosomal rearrangements. Retrotransposition is the mechanism by which Ty elements achieve their biased transmission and infective spread (there is another type of nuclear mobile element, transposons, which use a different, DNA-mediated mechanism, but they are not found in yeast genomes). Ploidy is one of the most fundamental features of genome structure, but as with sex, there is still no widely accepted explanation for the observed variation in ploidy. heterozygosity is certainly more than just an indicator of diploidy.

Citation: Zeyl C. 2007. Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment, p 507-525. In Heitman J, Kronstad J, Taylor J, Casselton L (ed), Sex in Fungi. ASM Press, Washington, DC. doi: 10.1128/9781555815837.ch31
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Figure 31.1

Nuclear-mitochondrial epistasis for fitness. Dashed lines and circles represent ancestral nuclear and mitochondrial genomes, respectively; solid lines and circles represent evolved genomes.

Citation: Zeyl C. 2007. Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment, p 507-525. In Heitman J, Kronstad J, Taylor J, Casselton L (ed), Sex in Fungi. ASM Press, Washington, DC. doi: 10.1128/9781555815837.ch31
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Image of Figure 31.2
Figure 31.2

Schematic depiction of the population dynamics of parasitic DNA. (A) In asexual populations, selection opposes the increase in frequency of parasitic DNA. (B) In sexual populations, cycles of mating and meiosis enable parasitic DNA to spread despite selection, by infecting new lineages.

Citation: Zeyl C. 2007. Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment, p 507-525. In Heitman J, Kronstad J, Taylor J, Casselton L (ed), Sex in Fungi. ASM Press, Washington, DC. doi: 10.1128/9781555815837.ch31
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Figure 31.3

Tolerable fitness costs for genetic parasites () as a function of their rates of transmission by both mating types or genders ( + α)

Citation: Zeyl C. 2007. Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment, p 507-525. In Heitman J, Kronstad J, Taylor J, Casselton L (ed), Sex in Fungi. ASM Press, Washington, DC. doi: 10.1128/9781555815837.ch31
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