Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
Biochem Soc Trans. 2010 Oct;38(5):1210-4. doi: 10.1042/BST0381210.
Control analysis can be used to try to understand why (quantitatively) systems are the way that they are, from rate constants within proteins to the relative amount of different tissues in organisms. Many biological parameters appear to be optimized to maximize rates under the constraint of minimizing space utilization. For any biological process with multiple steps that compete for control in series, evolution by natural selection will tend to even out the control exerted by each step. This is for two reasons: (i) shared control maximizes the flux for minimum protein concentration, and (ii) the selection pressure on any step is proportional to its control, and selection will, by increasing the rate of a step (relative to other steps), decrease its control over a pathway. The control coefficient of a parameter P over fitness can be defined as (∂N/N)/(∂P/P), where N is the number of individuals in the population, and ∂N is the change in that number as a result of the change in P. This control coefficient is equal to the selection pressure on P. I argue that biological systems optimized by natural selection will conform to a principle of sufficiency, such that the control coefficient of all parameters over fitness is 0. Thus in an optimized system small changes in parameters will have a negligible effect on fitness. This principle naturally leads to (and is supported by) the dominance of wild-type alleles over null mutants.
控制分析可用于尝试理解为什么（定量地）系统是这样的，从蛋白质中的速率常数到生物体中不同组织的相对数量。许多生物参数似乎被优化为在最小化空间利用的约束下最大化速率。对于具有多个步骤且在串联中竞争控制的任何生物过程，自然选择的进化将倾向于使每个步骤施加的控制趋于均等。原因有二：（i）共享控制使最小蛋白浓度下的通量最大化，以及（ii）对任何步骤的选择压力与其控制成正比，选择将通过增加步骤的速率（相对于其他步骤），降低其对途径的控制。参数 P 对适合度的控制系数可以定义为 (∂N/N)/(∂P/P)，其中 N 是群体中的个体数量，∂N 是由于 P 的变化而导致的个体数量的变化。这个控制系数等于 P 的选择压力。我认为，自然选择优化的生物系统将符合充分性原则，即所有参数对适合度的控制系数均为 0。因此，在优化系统中，参数的微小变化对适合度的影响可以忽略不计。这个原则自然导致（并得到）野生型等位基因对 null 突变体的优势。
