文档介绍：Chapter 5
The Basic Properties of Quantitative Traits
Basic features of quantitative traits
Phenotypes are expressed as numerical values, called phenotypic values
Phenotypic values are obtained by measurements other than observation or counting
Phenotypic values behave continuous variation, usually follow normal or nearly normal distribution
Influenced by environments
Multiple factor (polygenic) hypothesis
Quantitative traits are influenced by many genes (polygenes)
Effects of individual genes are small (so that they can not cause discontinuity and can not be studied individually)
Infinitesimal ic model
Infinite number of genes
Infinitesimal small effect of each gene
Basic phenomena
Resemblance between relatives
depends on the relationship and the ic nature of the trait
Correlation between traits
pleiotropy, linkage
Inbreeding pressure and heterosis
especially for traits related to fitness and fertility
Measures of the population properties of quantitative traits
Mean
Variance
Covariance
Phenotypic value and genotypic value
The basic formula
P = G + E
environmental deviation
genotypic value
phenotypic value
(when there is no systematic environmental effects)
Basic model of genotypic value
Single locus
A2A2 A1A2 A1A1
-a 0 d a
Population mean
Multiple loci
Genotypic value
Often expressed as the deviation from the population mean:
Average effect of genes
The average effect of a gene is the deviation from the population mean of the mean genotypic value of the individuals which receive that gene from one parent, the gene from the other parent ing at random from the population.
Average effect of A1
Average effect of A2
Average effect of gene substitution
Change of population mean due to the replacement of A2 randomly taken from the population with A1