Tannenbaum Emmanuel
Department of Chemistry, Ben-Gurion University of the Negev, Beersheba, Israel.
Theory Biosci. 2009 May;128(2):85-96. doi: 10.1007/s12064-008-0054-8. Epub 2008 Dec 5.
This article develops a simplified set of models describing asexual and sexual replication in unicellular diploid organisms. The models assume organisms whose genomes consist of two chromosomes, where each chromosome is assumed to be functional if it is equal to some master sequence sigma(0), and non-functional otherwise. We review the previously studied case of selective mating, where it is assumed that only haploids with functional chromosomes can fuse, and also consider the case of random haploid fusion. When the cost for sex is small, as measured by the ratio of the characteristic haploid fusion time to the characteristic growth time, we find that sexual replication with random haploid fusion leads to a greater mean fitness for the population than a purely asexual strategy. However, independently of the cost for sex, we find that sexual replication with a selective mating strategy leads to a higher mean fitness than the random mating strategy. The results of this article are consistent with previous studies suggesting that sex is favored at intermediate mutation rates, for slowly replicating organisms, and at high population densities. Furthermore, the results of this article provide a basis for understanding sex as a stress response in unicellular organisms such as Saccharomyces cerevisiae (Baker's yeast).
本文开发了一组简化模型，用于描述单细胞二倍体生物中的无性和有性繁殖。这些模型假定生物的基因组由两条染色体组成，其中每条染色体若等于某个主序列σ(0)则假定为有功能的，否则为无功能的。我们回顾了之前研究的选择性交配情况，即假定只有具有功能染色体的单倍体才能融合，并且还考虑了随机单倍体融合的情况。当用特征性单倍体融合时间与特征性生长时间的比率来衡量时，若性别的成本较小，我们发现随机单倍体融合的有性繁殖比纯无性策略能为种群带来更高的平均适应性。然而，无论性别的成本如何，我们发现选择性交配策略的有性繁殖比随机交配策略能带来更高的平均适应性。本文的结果与之前的研究一致，这些研究表明，在中等突变率、对于缓慢繁殖的生物以及在高种群密度下，有性繁殖更受青睐。此外，本文的结果为理解诸如酿酒酵母（面包酵母）等单细胞生物中的有性繁殖作为一种应激反应提供了基础。
