Lenski R E
Biotechnology. 1991;15:173-92. doi: 10.1016/b978-0-409-90199-3.50015-2.
Fitness represents the combined effects of all other phenotypic properties on the capacity for survival and reproduction by a particular genotype in a particular environment. For most environmental application of genetically modified microorganisms, efficacy will be enhanced if the engineered genotype is more fit than its wild-type counterpart in the target environment. However, inadvertent spread of the engineered genotype will be less likely if it is less fit than the wild-type. Thus, the fate of a population of genetically engineered microorganisms, and the likelihood and magnitude of any environmental effects (whether beneficial or detrimental), will be strongly influenced by the relative fitnesses of modified and unmodified genotypes. In this chapter, I have presented theoretical principles and empirical methods for determining the relative fitnesses of engineered and wild-type clones. Selection coefficients were used to provide a quantitative measure of the difference in fitness between the two clones in a particular environment. Many engineered genotypes are unstable, such that their frequencies decline with time. Instability may be caused by infidelity of replication or transmission of a particular gene (which is termed segregation), or it may be caused by a difference in the fitness of genotypes that retain or have lost that gene (selection). In this chapter, I have also presented theoretical principles and empirical methods for distinguishing the effects of selection and segregation. Finally, it should be emphasized that selection coefficients and segregation rates can be estimated not only in highly simplified laboratory systems, but also in more complex natural or semi-natural systems, such as microcosms. All that is required is the ability to monitor the relative abundance of two clones (e.g., engineered and wild-type) that share a common environment.
适合度代表了在特定环境中，所有其他表型特性对特定基因型生存和繁殖能力的综合影响。对于转基因微生物在大多数环境中的应用而言，如果工程化基因型在目标环境中比其野生型对应物更具适合度，那么其功效将会增强。然而，如果工程化基因型的适合度低于野生型，那么其意外传播的可能性就会较小。因此，转基因微生物群体的命运以及任何环境影响（无论是有益的还是有害的）的可能性和程度，将受到修饰和未修饰基因型相对适合度的强烈影响。在本章中，我阐述了用于确定工程化克隆和野生型克隆相对适合度的理论原理和实证方法。选择系数被用来定量衡量在特定环境中两个克隆适合度的差异。许多工程化基因型是不稳定的，以至于它们的频率会随时间下降。不稳定性可能是由特定基因复制或传递的不忠实性（这被称为分离）引起的，也可能是由保留或丢失该基因的基因型在适合度上的差异（选择）导致的。在本章中，我还阐述了区分选择和分离效应的理论原理和实证方法。最后，应该强调的是，选择系数和分离率不仅可以在高度简化的实验室系统中估计，也可以在更复杂的自然或半自然系统中估计，比如微观世界。所需要的只是监测共享共同环境的两个克隆（例如，工程化克隆和野生型克隆）相对丰度的能力。
