The purpose of this Roundtable was to present in a condensed form the various problems posed to scientists and to breeders of farm animals by genes with large effect on quantitative traits, illustrating general considerations by the most typical examples of major genes form in species of economic importance.

First Dr R.C. Roberts and C. Smith's paper (from Edinburgh) is a general introduction to the subject, covering a broad range of theoretical and applied aspects in a compact and very clear form for a non-specialist After recalling that in the past little attention and importance was attributed to genes with large effect in animal breeding, the authors review the various methods which have been suggested for detection of such genes in animal populations. The purely statistical methods, based in some way on analysis of frequency distributions, are not of a high efficiency (although screening of extreme variants should not be neglected), and the safest approach is still that starting from "marker" genes identified by a qualitative effect, preferably if there are some hints on their physio-biochemical implications.

A few examples drawn from laboratory species or from plants suggests some directions of .research also on large animals. In connection with problems of detection or screeming, mention is done of difficulties in incorporating genetic material of foreign and less productive origin into populations with high level of performance. Genetic engineering might be in the future a solution for avoiding introducing undesired genetic material besides the desired gene. Then for exploitation of a gene with large effects in a breeding program, different strategies are to be followed according to particular features of the gene effects at a quantitative level.

P. Merat

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 6. Round tables, , 417-419, 1982
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