Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 171

The magnitude of heritability estimates depends on the genetic population used, sample size, and the method of estimation.

 Genetic populationWhen heritability is defined as h2 = VA/VP (i.e. in the narrow sense), the variances are those of individuals in the population. However, in plant breeding, certain traits such as yield are usually measured on plot (not on individual plants) basis. The amount of genotypic variance present for a trait in a population influences estimates of heritability. Parents are responsible for the genetic structure of populations they produce. More divergent parents yield a population that is more genetically variable. Inbreeding tends to increase the magnitude of genetic variance among individuals in the population. This means that estimates derived from F2 will differ from, say, those from F6.

 Sample sizeBecause it is impractical to measure all individuals in a large population, heritabilities are estimated from sample data. To obtain the true genetic variance for a valid estimate of the true heritability of the trait, the sampling should be random. A weakness in heritability estimates stems from bias and lack of statistical precision.

 Methods of computationHeritabilities are estimated by several methods that use different genetic populations and produce estimates that may vary. Common methods include parent–offspring regression and variance component method. Mating schemes are carefully designed to enable the total genetic variance to be partitioned.