Lande R
Department of Biology, University of Oregon, Eugene 97403-1210, USA.
Genetica. 1998;102-103(1-6):21-7.
A model is developed for alternate fixations of mildly deleterious and wild-type alleles arising by forward and reverse mutation in a finite population. For almost all parameter values, this gives an equilibrium load that agrees closely with the general expression derived from diffusion theory. Nearly neutral mutations with selection coefficient a few times larger than 1/(2N(e)) do the most damage by increasing the equilibrium load. The model of alternate fixations facilitates dynamical analysis of the expected load and the mean time to extinction in a population that has been suddenly reduced from a very large size to a small size. Reverse mutation can substantially improve population viability, increasing the mean time to extinction by an order of magnitude or more, but because many mutations are irreversible the effects may not be large. Populations with initially high mean fitness and small effective size, N(e) below a few hundred individuals, may be at serious risk of extinction from fixation of deleterious mutations within 10(3) to 10(4) generations.
我们构建了一个模型，用于研究在有限种群中，通过正向和反向突变产生的轻度有害等位基因和野生型等位基因的交替固定情况。对于几乎所有的参数值，该模型得出的平衡负荷与从扩散理论推导的一般表达式非常吻合。选择系数比1/(2N(e))大几倍的近中性突变，通过增加平衡负荷造成的危害最大。交替固定模型有助于对预期负荷以及种群从非常大的规模突然减小到小规模后的平均灭绝时间进行动态分析。反向突变可以显著提高种群的生存能力，将平均灭绝时间增加一个数量级或更多，但由于许多突变是不可逆的，其影响可能不会很大。初始平均适合度高且有效大小N(e)低于几百个个体的种群，可能在10³至10⁴代内由于有害突变的固定而面临严重的灭绝风险。
