Phenotypic value

We assume that the fitness of an individual with phenotypic value / is determined by a function W f, /), which is defined as follows ... 

The environmental deviation acts on the genotypic values - a and + a as a Gaussian noise, so that the phenotypic values of the individuals of the... 

Oi and 02 measures of the environmental effect which causes the observed spread of the phenotypic values. 

FIGURE 20.2 Illustration of QTL mapping. (Top) Circles indicate phenotype values for tested mice, with the values separated by mice harboring either the major or minor allele at the indicated locus. Panels correspond to gene regions as indicated by the black line. (Bottom) Manhattan plot showing location of a QTL on Chr 3. Reproduced with permission of Daniel Gatti, The Jackson Laboratory. 

All of the different types of results above presented lead to the conclusion that the influence of environmental deviations on the yield of individual plants is very high and almost completely masks the genotypic value that generally we seek. We have also observed similar results in other trials with other varieties. However, more important is the fact that these results are highly predictable based on the theory of quantitative genetics. Indeed, yield and virtually all of the economically important grapevine traits are quantitative traits for which phenotypic value (P) is in part determined by the genotypic value (G) and in part by an environmental deviation (E),... 

Harrigan PR, Montaner JS, Wegner SA, Verbiest W, Miller V, Wood R, Larder BA (2001) Worldwide variation in HlV-1 phenotypic susceptibility in untreated individuals biologically relevant values for resistance testing. Aids 15 1671-1677... 

We are, then, faced with breeding to improve something which consists of a multiplicity of contributing factors. The overall phenotypic performance of a plant may thus be a poor indicator of its genetic value in improvement. 

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