july 07
in aquaculture, selection is not commonly used propably because of poor extension of knowledge from researchers to farmer. However, selection is the efficient method in animal breeding programs because it can lead to the long term goals of genetic improvement.
the objective of selection is to change the average performance of a population for the same spesific trait by increasing the frequency of alleles that influence the trait in a desirable manner, that is, increase the frequency of the plus alleles. however, selection must be based on the observed performance of individuals. therefore, our ability to identify genetically superior individuals depends on the heritability of the trait.
the heritability of a metric character is one of its most important properties. it is defined as the ratio of additive genetic variance to phenotypic variance. the heritability is estimated from the degree resemble between relative.
growth is an easy parameter for phenotypic measurement. it can be measured as change in length or weight which is defined as growth. growth rate is perhaps the most important trait of interest in food fish culture.
to describe the change of the genetic properties from one generation to the next we have to compare successive generations at the some point in the life-cycle of the individuals, and this point is fixed by the age at which the character under study is measured. the change produced by selection that chiefly interests us is the change of population mean. this is the respon to selection, which will be symbolized by R; it is the difference of means phenotypic value between the offspring of the selected. the measure of the selection applied is the average superiority of the selected parents, which is called the selection differential, S; it is mean phenotypic value of the individuals selected as parents expressed as a deviation from the population mean, that is from the mean phenotypic value of all the individuals in the parental generation before selection was made.
in the selected population, the ratio of response to selection differential is equal to heritability. this parameter is called the realized heratibility: h2 = R/S
recapped from: Supattra Uraiwan
juragan@9300i.bkk