Indian Society of Genetics & Plant Breeding

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BREEDING FOR QUANTITATIVE CHARACTERS IN LINSEED. II. GENETIC CORRELATIONS AND CORRELATED GENETIC RESPONSE WITH SPECIAL REFERENCE TO TILLERING AND EARLINESS

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THE existence of correlated responses in the form of alterations in unselected
characters as a result of selection pressure exerted on a particular character has been
recognised for a long time by evolutionists' and geneticists. Thus, Darwin in his
, Origin of Species' writes " Hence, if man goes on selecting and thus augmenting
any peculiarity, he will almost certainly modify unintentionally other parts of the
structure owing to the mysterious laws of correlation." With the developments in
our understanding of heredity that followed the re-discovery of Mendel's work in 1900,
we are now in a position to have some idea of the reasons behind these mysterious laws.
Human or natural selection is based on the phenotype as a whole and not on any
particular character in isolation. Such selection, is, therefore, based to a large extent
on the preservation of the complete genotypes of individuals having the favoured
phenotype. It follows that, consequent on such selection, genes not affecting the
particular character being selected for will also be exposed to a selection pressure,
the magnitude of which will depend on the contribution of these unselected genes
towards the fitness of the organism as a whole. The existence of such an indirect
selection, as a result of the physical and biochemical relationship between the gene
or gene-complex being selected and others, is responsible for what Darwin terms the
"mysterious laws of correlation". The mechanism underlying such correlated responses has become much clearer following the formulation of the theory of polygenic
control of continuous variation by Mather (1949) and has been considered in great
detail by Wigan and Mather (1942) and Mather and Harrison (1949). The literature on this aspect has been reviewed extensively by Haskell (1954) and Sisodia (1960).
  

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Year: 1961
Volume: 21
Issue: 2
Article DOI: NA
Print ISSN: 0019-5200
Online ISSN: 0975-6906

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