Several works published in recent years concerned the possible genetic component of phenotypic variability in livestock. Although all of them dealt with the genetic of variability, some were connected with plasticity, which is the ability to modulate the mean level of performance according to the environment. Other studies dealt with performance stability over different environments or with canalising selection (canalisation) which strives to obtain an homogenous population around an optimal average. These studies assumed different genetic hypotheses to explain the genetic control of variability and particularly the natural stability : a) Heterozygous individuals are best suited to fit variation of environments (Gillepsie and Turelli, 1989) ; b) Some genes which control the mean of a trait can also act on fitness, with overdominance effect (Robertson 1956) ; c) Due to pleiotropic effects, alleles of some genes controlling the mean can lead to different phenotypic expressions in different environments (Via and Lande, 1985) ; d) Mean and variability of a trait are under the control of different genes (Scheiner and Lyman, 1991). Experimental results confirm the existence of plasticity genes (Gibson and Hogness, 1986 ; Reilly et al., 1991 ; Lukens and Doebley, 1999).
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 19, , 19.03, 2002
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