A Study On The Expansion Of Segregation Analysis In The Inheritance Of Quantitative Traits In Plants

Quantitative genetics is a principle and applied science,which according to inheritance principles applied proper inheritance model and the principles and methods of mathematical statistics to discuss genetic basis of quantity traits variation among individuals in biotic population and studied the transitive rules of quantity traits and application in biological improvement.However,modern quantitative genetics is a science of genetic basis and inheritance of revealing quantity variant at molecular level.Using the method of mathematical statistics to mark the molecular and to analyze the phenotype measured data combination is called molecular quantitative genetics.By re-analysing the original data from the QTL location and new statistical tools,the control genes of quantitative trait exist lots of differences in the effect,relatively large effect gene expresses characteristics of a major gene,relatively small effect gene expresses characteristics of minor polygenes,and inheritance model is a model type between major-polygene mixed inheritance models.Gai et al(1998) developed the system of inheritance of quantitative traits in plants to study the major-polygene mixed inheritance models by using the theory of mixture distribution,maximum likelihood estimate,EM algorithm and the IECM algorithm.The research is the improvement of inheritance of quantitative traits in plants.First, improved the condition maximization part of ECM algorithm,let the environment variance stable and formed local iterative ECM algorithm.This method is called JECM algorithm.Second,united the individual separation of generation and non-united generation, use this method,the development of major-polygene mixed inheritance models from 1-2 major-polygene mixed inheritance models to the mixed 3 major-polygene mixed inheritance models with a chain by EM algorithm and JECM algorithm(including the chain between two genes and inter-chain among three genes).The main results obtained are:1.Complying with the principles of quantitative genetics,variance components distribution segregation populations were partitioned into major-gene,error and environmental variance.Use the Lagrange multiplier method and the JECM algorithm to estimate the composition distribution parameters of mixed distribution.Steps are as follows:â‘ choose initial values for parameters according to the observation,including:the initial valueμ⁽⁰⁾ of distribution average,the initial valueσ²⁽⁰⁾ of environmental variance and the initial valueσ_j0²⁽⁰⁾ of polygenes variance;â‘¡In order to obtain complete information on the expectations of the log-likelihood function L_C((?)),implement the E steps,to obtain posterior probabilityω_jit;(3) CM1 steps:fixσ_j0²⁽⁰⁾,σ²⁽⁰⁾,obtain the maximum likelihood function valueμ⁽¹⁾ of distribution average;CM2 steps:fixμ⁽¹⁾,σ_j0²⁽⁰⁾,obtain the maximum likelihood function valueσ²⁽¹⁾ of environmental variance;CM3 steps:fixμ⁽¹⁾,σ²⁽¹⁾,obtain the maximum likelihood function valueσ_j0²⁽¹⁾ of polygenes variance,â‘£let estimated value of the distribution parameters fromâ‘¢as the initial value,repeat CM1 step,CM3 step inâ‘¢,until the difference very small between adjacent maximum log-likelihood function value.2.Based on the 1-2 major-polygene mixed inheritance model,for F₂ groups,set up mixed inheritance model with 3 pairs on a chain(in A,B,C,A,B chain and A,B,C inter-chain) of 12 kinds of major genes,so that the development of genetic models to seven categories of 34 species,through the genetic data analysis of sorghum restorer 591×560 portfolio flowering period,sorghum flowering period is controlled by three chain pairs of major genes(A,B chain),in line with the additive - dominance - epistatic model,the major gene of the first and the second pair was negative overdominant,the third was partly dominant.The inheritance rate of major genes is 66.99%.For P1,F1,P2,B₁+B₂ of generation united,set up 5 kinds of major-polygene mixed inheritance models with 3 pairs on a chain(in A,B,C,A,B chain),so that the development of genetic models six categories of 28 species.through the flowering period data of rape (Ningyou No.7×Nonglin No.41) BC₁F₁ combinations confirmed that rape flowering period is controled by three chain pairs of major genes(A,B chain),in line with the additive -dominance model,the first major genes were additive,the second was completely dominant, the third was negative completely dominant.The inheritance rate of major genes of B₁ groups is 78.83%and the inheritance rate of major genes of B₂ groups is 85.25%.For P₁,F₁,P₂,F_2:3 of generation united,set up 3 kinds of major-polygene mixed inheritance models with 3 pairs on a chain(in A,B,C,A,B chain),so that the development of genetic models six categories of 28 species;For P₁,F₁,P₂,B_1:2+B_2:2 of generation united,set up 5 kinds of major-polygene mixed inheritance models with 3 pairs on a chain(in A,B,C,A,B chain),so that the development of genetic models six categories of 26 species, through erucic acid test data of the flowering period data of rape HSTC14(P₁)×Ningyou No.7(P₂) combination of F_2:3 families confirmed that rape HSTC14×Ningyou No.7 combination of F_2:3 families in line with the additive-dominance- epistatic model,the first major genes were negative completely dominant,the second were partly dominant,the third were negative overdominant.The inheritance rate of major genes is 56.55%.3.According to the procedures,possible genetic models with one to three major genes were used to fit the distribution of segregation population.Goodness-of-fit were used to select the most fitted model of major genes.Because the family average error is less than observation error of the single,a number of separating the joint generations segregation analysis is superior to the individual generations segregation,use of the adding of homogeneous groups(P1,P2 and F1),to identify the exist of polygenes and then,determine the inheritance model of quantitative traits.Judging from the examples,using of the joint analysis of a single separation generation and non-separation can improve the estimation accuracy of additive and dominant effect of major genes,and reveal more genetic information.4.It is proved JECM algorithm algorithm though 20 times repeat Monte Carlo simulation experiment and IECM algorithm to select the consistency of most appropriate inheritance model.5.Computer programmes were written in MATLAB 7.0,and then compiled and linked into executive files. This study improve and simplify the parameter estimation methods of separation and analysis,enriching the inheritance model of the system of inheritance of quantitative traits in plants and further improve the system.