11 Meiosis and Sporulation in Saccharomyces cerevisiae

Abstract

I. INTRODUCTION
A. The Importance of Meiosis
Meiosis has a central role in the sexual reproduction of nearly all eukaryotes. The major genetic events that occur during this process are critical for generating genetic diversity and producing offspring with normal chromosome numbers. The stages and transition periods in the two successive divisions that comprise the process are exquisitely regulated and differ significantly in timing and chromosome behavior from the corresponding stages of mitosis. The first division deviates most dramatically from mitotic cell division in its prolonged DNA S phase, greatly extended prophase in which homologous pairing and recombination occur, anaphase cohesion of sister chromatids, and disjunction of homologs (for review, see Baker et al. 1976). In contrast, the second meiotic division has a shortened G₁, lacks its own S and G₂ phases, and is otherwise similar to mitosis, utilizing many of the same gene products to disjoin the previously replicated sister chromatids. These dramatic changes in chromosome behavior offer a fascinating look at the regulatory mechanisms that control both cell division and cell differentiation. For example, what triggers meiotic development? Is there a single irreversible commitment point similar to mitotic Start for all meiotic events? How does the synaptonemal complex develop and what specific role(s) does it have in meiosis? What factors regulate the assembly of meiosis I and meiosis II spindles and the pattern of chromosome segregation in each division? How is the progression of events coordinated through two meiotic divisions? Do they function on a single sequential dependent...