杂种优势的遗传力理论及其对全球农业的意义

文中一开始就以遗传力概念来推翻杂交育种中的配合力概念。理由是一般配合力随基础群中品种类别和数目的改变而改变，因而特殊配合力也随之而变。因而用不同纯系品种作试验的基础群的结果也不能相比较。因而，配合力不能用来作为参数用以预测下一代的杂种效果。另一方面，对于每一杂交组合有一个分别的遗传力可以在杂交育种中应用，就象在纯系育种中应用一样。由于这同一概念可以同样在二者中加以应用，任何其他概念都是不必要的了。因而配合力概念必须予以摈弃。另一在原文中未加说明的原因是，用配合力概念需要无穷多个品系才能和遗传力的结果相比较，仅此一点就把配合力的作用排斥掉了。文中的主题是杂种优势老大难题可以用笛卡尔的推理方法来解决。从杂种优势的定义出发H：F1-MP，在此，H＝杂种优势，F1为子一代，MP为亲本平均数或中亲。由一个二项分布随机变数及其推广至多项分布推导出杂种优势的公式：VF1=Na^2/2 Md^2/4 VI(F1)加性 显性 F1上位 VMP=Na^2/ V1/2 加性 亲代上位VH=Nd^2/4 VI(F1) V1/2 显性 Fl上位 亲代上位 在此N=控制性状的基因数，a=(Pi-Pj)/2,d=离中亲的偏差，而各方差则如方程底部所列。于是这些项目都可由资料算出，以致问题变得简单到任何大学生都能解决。换言之，当提问正确时，正确的答案便可以求得。谁曾经证明过遗传力的理论不能应用于杂交育种中，例如在两个纯种的杂交子一代中呢?从这一启示出发，我们发现，两纯系杂交的子一代是一个孟德尔群体，其中p,q均为1／2，这样就简化了问题。我们的杂种优势的遗传力理论(HTH)的形成是基于以下两点：1)既然严p q=0.5 0.5=1，那么两个纯系杂交只是纯系育种的一个特例，因而F1的遗传力必定存在。2)分析中，我们只需找出计算这个参数的方法，这很容易。因为它就等于加性效应组分除以VF1，即(1／2)Na^2/VF1，这可以从杂种优势方程导出。20世纪末，我们成功地解决了杂种优势这个难题。同时我们还发现，杂种遗传力，这个新的遗传参数，它的大小随杂交次数的增加而增加，从而将育种与进化联系起来，它把我们带进了一个新的时代——进化工程时代；向我们展现了一个新的天地，即人工选择的作用最终必将超越自然选择，同时将漫长的时间大大缩短。另外，对于农业它可以将众多理想基因集中于杂种，使食物产量不断的增加，这是过去“将基因固定的理论”所不能解决的。这样作人工选择，对于相同的进展，可以将我们的时间、劳力和成本节省约80％。如果应用于各种农作物包括杂交水稻，产量将会有更大规模的提高。实际上，如果我们的科研教育单位能及早的利用它，必将会掀起一场前所未有的新的绿色革命。至于进化工程会把我们领入一个什么样的未来，这个问题就留给科幻小说家们去描绘吧。

The Heritability Theory of Heterosis and Its Meaning for Global Agriculture

This paper begins with the overthrow of the concept of combining ability in crossbreeding by the concept of heritability.The reason is that general combining ability changes with the number and kind of pure strains in the foundation stock and hence special combining ability changes also,so that work with different kinds of pure strains in the foundation stock cannot be compared.Hence combining ability is useless as a parameter to predict the amount of heterosis expected in the next generation. On the other hand,since each cross has a separate heritability,it can be applied to a cross population just as successfully as in purebreeding.Since the same concept holds in both cases,resort to any other concept would be superfluous.That's why combining ability must be rejected.Another reason (not given in the full text) is,an infinite number of pure strains would be required in the foundation stock for its results to be comparable with those of the heritability theory,which disposes of its utility altogether.The main content of the thesis is then the centennial enigma of heterosis can be resolved by Descarte's theoretic method of deduction.Accordingly we start from the definition of heterosis H=F1-MP,where H is heterosis,F1 is the first generation offspring,MP is the mean of the parents or midparent,and from the use of a binomial random variable and its extention to the multinomial case derive the basic relations of heterosis with its components.Starting with second degree statistics,we obtain VH=VF1-2cov(F1,MP)+VMP,where V and cov stand for variance and covariance.The equations of heterosis areVF1=(1/2)Na2+(1/4)Nd2+VI(F1),additive dominance F1 epistasisVMP=(1/2)Na2+(1/2)VI,additive parental epistasisVH=(1/4)Nd2+VI(F1)+(1/2)VI,dominance F1 epistasis parental epistasis.where N is number of genes controlling a trait,a=(Pi-Pj)/2,d is deviation from midparent,while the variance components are all indicated by their names under the repective terms.It turns out that all these can be easily computed from the data so that the problem becomes a simple one which any college student may solve.In other words,the right answers are found when the right questions are asked.Who had ever shown that the heritability principle is inapplicable in crossbreeding,e.g.,in a crossing of two pure strains?From this cue arose the realization that the F1 of a cross of two pure strains must also be a Mendelian population,with p and q both equal to 1/2 which simplifies the algebra outright.This Heritability Theory of Heterosis,or HTH in capital letters,rests on 2 initial arguments:1) Since 0.5+0.5=1,crossing two pure strains gives a population which is only a special case of purebreeding,therefore a heritability coefficient must exist for the F1;2) Our problem reduces to that of finding that coefficient;the answer is given by the additive component divided by VF1,i.e.,(1/2)Na2/VF1.which is readily found from the solution of the heterosis equations.Thus the eternal enigma of heterosis is resolved!This happened at the end of the 20th century.We now come to the second point of the discovery,the new genetic parameter crossheritability which will rise in size with the increase of the number of times it's used and form the link between breeding and evolution.The advent of the Age of Evolution Engineering in the 21st century marks a totally new era,showing that artificial will ultimately supercede natural selection,with the long span of time element eliminated.For agriculture at least,it means there is no limit to the increase of food supply by the new method,with the concentration of desirable genes by hybridization in place of the old theory of their fixation.Genetic gain is achieved through artificial selection,with an 80% saving of time,labor and cost by adoption of the new method. Applied to a further increase in all kinds of agricultural products including hybrid rice,it means that a huge escalation,in fact a New Green Revolution,on a much larger scale than that of any such before,is in view,provided it is adopted in our research and educational institutions as early as possible,ere its spread elsewhere.The possibilities from the evolution point of view can only be pictured by science fiction.