The potential for genetic gains in your program
The breeder's equation
A well-structured breeding program will improve the genetic quality of your broodstock population stepwise for each new generation. The genetic gain per generation is influenced by several factors, as explained by an extended breeder’s equation.
An effective selection requires a broad genetic variation within the breeding population. The effect on selection depends on the amount of additive genetic variance and not on the genetic variance in general. Thus, it is important to ensure that the breeding population maintains a high level of additive genetic variation for all interesting traits.
The selection intensity represents the difference between the mean of the selected individuals and the mean of the population, measured in units of the population’s phenotypic standard deviation. The selection intensity will depend on the number of individuals (breeding candidates) available for selection. As the selection intensity increases, so does the selection response.
The accuracy of selection indicates how well the selection criteria represent the selected breeding candidates’ true breeding values. Selection based on the breeding candidates’ performance is very efficient for traits with medium to high heritability estimates (i.e. growth). The accuracy of selecting traits with a low heritability is increased by using additional full- and half-sib information.
Selection based on genomic data (i.e. genomic selection) may considerably increase selection accuracy, especially for traits with low heritability. However, genotyping’s high costs will often restrict the number of genotyped breeding candidates available for selection. Thus, care should be made to avoid a reduction in the selection intensity cancels the increased accuracy of genomic selection.
The generation interval is the average age of the breeding candidates at the birth of their offspring, which will produce the next generation of breeding candidates. The generation interval facilitates the calculation of selection responses per year instead of per generation. Efficient breeding programs should minimize the generation interval.
Most populations have several deleterious recessive alleles hidden in heterozygotes at low frequencies (referred to as a population’s genetic load). Inbreeding, i.e. the mating between individuals related by ancestry, will unmask these deleterious recessive alleles and cause inbreeding depression observed as reduced biological fitness. Thus, efforts should be made to restrict the accumulation of inbreeding in breeding populations.
Through selection, we are improving the population mean for important production efficiency and disease traits.
By selective breeding we can reduce the frequency of unwanted genes and increase the frequency of desired genes.
A well-designed programme can significantly improve the genetic gain for each generation, illustrated by the movement of the population mean for growth in the Progift Nile tilapia programme though 13 generations of selective breedig. Akvaforsk Genetics Center (AFGC), now Benchmark Genetics, has been involved as consultant in this programme since the start. Interestingly, the largest animals in the base population are far smaller (about 250 gr) than the smallest animals in the F-12 generations.
By using our expertise, systems and technologies, we are tailoring our services to help our clients optimize the genetic gains of their programmes. If you want to learn more about how we can assist you in taking out the genetic potential of your breeding programme, please contact us today.