Selection during a selfing programme. I. The effects of a single round of selection.

Theory is presented to describe the effects of a single round of selection during a selfing programme in terms of both the mean and the genetical variance of the inbred lines produced. Response equations describing the effect on the inbred means are used to determine optimum breeding designs in a limited set of circumstances. These theoretical arguments are supported by computer simulations, and good agreement with expectation is found. The magnitude and direction of dominance is shown to be unimportant even in the case of early generation selection. A description of the reduction in genetic variance between selected lines is also presented and supported by simulation. Unlike the effects described by Bulmer in outbreeding populations, this reduction is fixed during a selfing programme. The simulation studies show that the additional variance generated by further segregation after selection may also be affected by selection, but the assumption that it is unaffected is found to be adequate.