According to the fitness of heterozygote was lower than homozygote among panmictic population,the process of generational accumulate of mutant gene r was considered.Branch point of r＇s frequency by generational evolution which revealed the hereditary incompatibility between R and r,was worked out,and it was found that genetic drift can make r have higher frequency to surpass the branch point to form reproductive isolation.It was not enough to have the three conditions of mutation,genetic drift and natural selection to be the drive of biological evolution;hybrid weakness,the repelling interaction between the genetic background of original population and the new mutation,were also needed.
[Objective]The aim was to discuss elimination mechanism and equilibrium model about complete linkage gene of panmixis based on fitness.[Method]A mathematical model that gsgenerational evalution of frequency of panmixis two pairs of complete linkage gene under difference fitness was built by using difference equations to study elimination mechanism and genetic equilibrium state of panncticcoinplete linkage gene.[Result]The panmixis is different from Hardy-Weinberg Equilibrium which reached the equilibrium just by one generation.A method that by using linear equation to calculate the frequency of four gametes and the fitnessed of panmixis was established after detormining is the fitness of 10 genotypes the necessary and sufficient condition of the panmixis to reach balance.[Conclusion]The method is valuable for reference on linkage disequilibrium and hitchhiking effect study.
Upon the analogy of definition of heterosis and inbreeding depresstion in terms of population genetics, the heterosis is thought to be evaluated overall with fitness. By establishing a mathematical model, the equilibrium status of three genotypes of random mating population （i. e. RR, Rr and rr） under different fitness, which exposes that heterosis is the precondition for multiallele to exist in the population. The heterosis protects the genetic diversity and makes the population owning a stronger self-control and evolution potential by improving the hetemzygote＇s fithess so as not to wash out different types of genes. It deepens Darwin＇s thoughts of individual section by making the individual fitness consonant with population fitness.
The study researched the inbred population which three genotypes of each pair heterozygous gene with different fitness. Change law by generations of genotype ratio was reflected by difference equations. The result showed that the genotype ratio that parents were all heterozygous population tended to balance, about needing 15 generations. The fitness of Rr was over or equal to two times of RR＇s or rr, which was the condition of Rr could be reserved for a long time.
