遗传学英文课件：10 复杂性状遗传.pptVIP

* Inheritance of Complex Traits * Our ability to make predictions about an offspring’s phenotype is improved in situations where the genotypes are not confused by dominance. Consider, for example, the inheritance of flower color in the snapdragon. 环境因素对金鱼草的花色也没有影响 影响花色的原因是门德尔的分离律 * Inheritance of Complex Traits * Quantitative geneticists distinguish between genetic variance that is due to alleles that act additively and genetic variance that is due to dominance. These different variance components are symbolized as: Va= additive genetic variance Vd= dominance variance Vi= epistatic variance Epistatic interactions, like dominance, are of little help in predicting phenotype. * Inheritance of Complex Traits * Altogether, these three variance components constitute the total genetic variance: Vg = Va + Vd + Vi If we recall that VT=Vg+Ve, we can express the total phenotypic variance as the sum of four components: VT= Va + Vd + Vi +Ve Of these four variance components, only the additive genetic variance, Va, is useful in predicting the phenotypes of offspring from the phenotypes of their parents. * Inheritance of Complex Traits * This variance, as a fraction of the total phenotypic variance, is called the narrow-sense heritability, symbolized h2. Thus, h2 =Va/VT Like the broad-sense heritability, h2 lies between 0 and 1. The closer it is to one, the greater is the proportion of the total phenotypic variance that is additive genetic variance, and the greater is our ability to predict an offspring’s phenotype. * Inheritance of Complex Traits * Human stature is highly heritable, but litter size (每窝的产子数) in pigs is not. Thus, if we knew the parental phenotypes, we would be better able to predict the height of a human’s offspring than litter size of a pig’s offspring. * Inheritance of Complex Traits * 5. Predicting Phenotypes Predicting an offspring’s phenotype based on the phenotypes of its parents and the narrow-sense heritability of trait. Only a portion of the deviation of