Breeding strategies

Abstract

The main objective in a breeding program is to move the mean value of the trait in the desired direction for a normally distributed trait, or for a trait with two (or more) discrete classes, such as survival, to increase the frequency of the desired class(es). Changes in the population mean or in class frequencies from one generation to the next are termed selection response. Selection response for a normally distributed trait is illustrated in Figure 7.4. Selection response or genetic gain can be obtained by applying different breeding strategies. For a long-term breeding objective, the only suitable strategy for a breeding nucleus will be some type of pure-breeding approach for additive genetic improvement. The breeding strategies that may be applied to produce commercial fry are less restricted than breeding within the nucleus. Any kind of crossbreeding, ploidy manipulations and sex manipulation, may be applied if the productivity of the commercial fry can be further improved. Any breeding strategy for commercial fry production that imposes limitation on the progress in additive genetic performance in the nucleus should be avoided (for example the use of highly inbred lines in a crossbreeding program, see below).