Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment

Clifford Zeyl

doi:10.1128/9781555815837.ch31

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

Author: Clifford Zeyl¹

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Affiliations: 1: Department of Biology, Wake Forest University, P.O. Box 7325, Winston-Salem, NC, 27109

Content Type: Monograph

Publication Year: 2007

Category: Fungi and Fungal Pathogenesis

Book DOI: 10.1128/9781555815837

Chapter DOI: 10.1128/9781555815837.ch31

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Abstract:

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 Saccharomyces cerevisiae establishes the potential for extensive inbreeding. A haploid yeast individual is one of two mating types, MATa or MATα 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. MAT 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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Ploidy and the Sexual Yeast Genome in Theory, Nature, and Experiment

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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.

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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.

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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.

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Figure 31.2

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Figure 31.3

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

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Figure 31.3

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

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