Quantitative genetics of intraspecies hybrids

Quantitative genetics generally is based on the properties of the randomly fertilized (RF) population or inbred derivatives of it. Simple hybrids and hybrid swarms do not conform to this model; and only some properties of hyb rid means appear to have been available. In this paper, several genetical p roperties are derived, including genotype and allele frequencies, genotypic variance, broad-sense heritability, and outbreeding coefficient. The earli er mean is confirmed, and hybrid vigour is examined critically. These resul ts make it possible to evaluate quantitatively both natural selection and f orward selection tin plant breeding) from hybrids, An important finding is that hybrids with maximum hybrid vigour do not maximize genetic advance fro m forward selection, i.e. evolution is unlikely to enhance hybrid vigour. A nother finding is that the concepts of additive generic variance and narrow -sense heritability are inappropriate for hybrids, owing to the genetic dis equilibrium inherent from their origin, and to the ephemeral nature of thei r population structure.