Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 172

The methods of estimating heritabilities have strengths and weaknesses.

 Variance ComponentsThe variance component method of estimating heritability uses the statistical procedure of analysis of variance. Variance estimates depends on the types of populations in the experiment. Estimating genetic components suffer from certain statistical weaknesses. Variances are less accurately estimated than means. Also, variances are unrobust and sensitive to departure from normality. An example of heritability estimate using F2, and backcross populations is as follows:Example:Using the data in the table below

	P1	P2	F1	F2	BC1	BC2
Mean	20.5	40.2	28.9	32.1	25.2	35.4
Variance	10.1	13.2	7.0	52.3	35.1	56.5

Broad sense heritability

Narrow sense heritability

Other methods of estimation

(The estimate is very close to that obtained by using the previous formula.)

 Parent–Offspring RegressionThe type of offspring determines if the estimate would be broad sense or narrow sense. This method is based on several assumptions: the trait of interest has diploid Mendelian inheritance; the population from which the parents originated is random‐mated; the population is in linkage equilibrium (or no linkage among loci controlling the trait); parents are non‐inbred; no environmental correlation between the performance of parents and offspring.The parent–offspring method of heritability is relatively straightforward. First, the parent and offspring means are obtained. Cross products of the paired values are used to compute the covariance. A regression of offspring on mid‐parent is then calculated. Heritability in the narrow sense is obtained as follows:where bop is the regression of offspring on mid‐parent, and VA and VP = additive variance, and phenotypic variance, respectively.However, if only one parent is known or relevant (e.g. a polycross):and h2 = 2bop