基于酵母生活周期〈动〉<动>的有性和无性复制策略的比较
A comparison of sexual and asexual replication strategies in a simplified model based on the yeast life cycle
摘要：
本文建立了描述{ \it Saccharomyces cerevisiae}中无性和有性复制途径的突变-选择平衡的简化数学模型。我们假设二倍体基因组由两条染色体组成，并且我们假设每条染色体是功能性的，当且仅当它的碱基序列与某个主序列相同。酵母细胞的生长和复制被建模为一阶过程，一阶生长速率常数由给定基因组是否由零个、一个或两个功能染色体组成来确定。在无性途径中，我们假设一个给定的二倍体细胞分裂成两个二倍体。在有性途径中，我们假设一个给定的二倍体细胞分裂成两个二倍体，每个二倍体又分裂成两个单倍体。由此产生的四个单倍体进入一个单倍体池，在那里它们生长和复制，直到它们遇到另一个与之融合的单倍体。当性行为的成本较低时，我们发现选择性交配策略导致种群的平均适应度最高，与所有其他策略相比。我们还表明，在低到中等的复制能力，随机交配的有性复制有一个更高的平均健身比无性复制，只要成本低。这与以前的工作表明，有性复制是有利的，在高人口密度，低复制率，和中间的复制重复率是一致的。本文的结果还表明{ \it S.酿酒酵母在受到压力时会从无性复制转变为有性复制，因为压力生长条件为酵母提供了从其基因组中清除有害突变的机会。
英文摘要：
This paper develops simplified mathematical models describing the mutation-selection balance for the asexual and sexual replication pathways in {\it Saccharomyces cerevisiae}. We assume diploid genomes consisting of two chromosomes, and we assume that each chromosome is functional if and only if its base sequence is identical to some master sequence. The growth and replication of the yeast cells is modeled as a first-order process, with first-order growth rate constants that are determined by whether a given genome consists of zero, one, or two functional chromosomes. In the asexual pathway, we assume that a given diploid cell divides into two diploids. In the sexual pathway, we assume that a given diploid cell divides into two diploids, each of which then divide into two haploids. The resulting four haploids enter a haploid pool, where they grow and replicate until they meet another haploid with which to fuse. When the cost for sex is low, we find that the selective mating strategy leads to the highest mean fitness of the population, when compared to all of the other strategies. We also show that, at low to intermediate replication fidelities, sexual replication with random mating has a higher mean fitness than asexual replication, as long as the cost for sex is low. This is consistent with previous work suggesting that sexual replication is advantageous at high population densities, low replication rates, and intermediate replication fidelities. The results of this paper also suggest that {\it S. cerevisiae} switches from asexual to sexual replication when stressed, because stressful growth conditions provide an opportunity for the yeast to clear out deleterious mutations from their genomes.
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