突变率计算中细菌群体生长不同步系数的修正

Modification the Synchrony Coefficient for Mutation Rate Calculating in Bacterial Population

遗传和变异是生物学最根本的问题之一,而突变率估算有助于比较不同基因、不同生物个体、以及不同生长环境下突变率的差异。细菌因其生长繁殖快速和群体庞大而成为突变率估算的最方便的模式生物。突变率的定义为:每个细胞每一世代发生突变的概率。通常表示为μ=Δm/ΔN。其中,Δm为突变数,ΔN为细菌分裂的世代数。国内外的微生物学及遗传学教科书和专著中,在计算细菌突变率时,有些引入了ln2作为群体中细菌分裂不同步的校正系数,有些则没有。那么,在突变率估算中,究竟是否应该对非同步生长群体进行校正?如果需要校正,仅仅引入ln2作为校正系数就可以了吗?本文在分析细菌指数生长的数学规律时,指出了细菌同步分裂和非同步分裂的差别,以及ln2的数学来源和生物学意义。实际上,ln2是细菌群体生长的代时和倍增时间之间的关系系数,即TG=ln2·TD,不能简单地将ln2理解为细菌分裂不同步的校正系数;并指出了在非同步群体中,细菌分裂的世代数通常由实验检测而得到,其本身已经包含了非同步因素,不能再次引入ln2进行校正;如果细菌分裂的世代数并非通过实验检测而得到,那么需要根据已知条件和细菌指数生长相关公式仔细计算,而不是简单地引入ln2作为不同步系数进行校正。

Heredity and variations are most essential problems in biology. 15stlmatmg me mutauon rates will be a great help for well understanding the difference among the different genes, different biological species, and under different growth environments. Bacteria are the best mode for estimating mutation rates due to their fast growth rates and their huge population sizes. Mutation rate （μ） is defined as the probability of mutation in each bacterial cell and each bacterial generation, usually expressed as μ= Δm / ΔN. Here, Δm is the number of mutations, and AN is the number of generations. In some famous microbiology and genetics textbooks and monographs, ln2, as the synchrony coefficient for non-synchronous bacterial population, was introduced into the mutation rates calculation formulae, but in others not. So, how to calculate the mutation rates in non-synchronous bacterial population？ Just introduce coefficient ln2 is enough？ In this essay, by analyzing the mathematical characteristics of exponential growth in bacterial population, both synchronous and non-synchronous, the biological meaning of ln2 was been well expressed, i.e., TG = ln 2. TD It means, in non-synchronous population, the ratio of generation time （TG） to doubling time （TD） is ln2. However, in ideal synchronous population, the generation time （TG） is equal to the doubling time （TD）. Because in non-synchronous population, the number of generations was usually estimated by the experimental data, these data had been already included the non-synchrony factor of the experimental population, it was no need to introduce ln2 as synchrony coefficient into mutation rates calculating formulae. If the number of generations was not estimated by experimental data, it was need to carefully calculate the value of generations based on the given data, rather than just introduced ln2 as synchrony coefficient into mutation rate cal-culating formulae.