A deterministic model to predict response with mass selection when a major locus is segregating is presented. The model uses a selection index framework in which the weight of the different components included in the index are adjusted to describe the different methods of selection using genotype information as selection criteria. The response over multiple generations to several methods of selection using either the whole genotype effect (genotypic methods) or only the Mendelian sampling deviation of the major locus (Mendelian methods) was compared with selection using only performance record (phenotypic method). Relevant differences in response between using and ignoring information on the major gene were observed only when the favourable allele was at a low frequency. When the major locus had a completely additive effect, all the genotypic or Mendelian methods had a higher cumulated genetic gain in the first 3-4 generations of selection but this advantage was lost thereafter. In the long term, without exception, all methods using genotype information of an additive major gene had lower cumulated gain than phenotypic selection over a wide range of parameters. The reason for the long-term loss, was a reduction in the intensity of selection applied to the polygenic background arising from increasing the differences in the selective advantage between genotype groups. The same trend was observed when the favourable allele of the major locus was completely recessive or dominant, with the exception of the cases of a large recessive locus (over one phenotypic standard deviation) where the extra early gain from using genotype information was maintained in the long term. This was explained by the inefficiency of the phenotypic selection to fix the favourable allele due to the linkage disequilibrium built-up between the major locus and the polygenic effects. Differences in the inbreeding rate were also observed between these methods: the genotypic methods had the highest inbreeding rate while the Mendelian had the lowest. The difference in the inbreeding rate was mainly observed in the first generations of selection and increased with lower starting frequency of the major locus. (C) Inra/Elsevier, Paris.
|Number of pages||25|
|Journal||Genetics Selection Evolution|
|Publication status||Published - 1998|
- major gene indices gain inbreeding loss marker-assisted selection quantitative traits animal populations information improvement efficiency simulation model