By Trygve Gjedrem

Even supposing aquaculture as a organic construction process has an extended heritage, systematic and effective breeding courses to enhance economically very important qualities within the farmed species have infrequently been applied until eventually lately, apart from salmonid species. which means the vast majority of aquaculture construction (more than ninety percent) is predicated on genetically unimproved shares. In livestock the placement is tremendously assorted: virtually no terrestrial farm construction is predicated on genetically unimproved and undomesticated populations. This distinction among aquaculture and cattle creation is despite the fact that the fundamental components of breeding conception are an analogous for fish and shellfish as for cattle. One attainable explanation for the adaptation is the complexity of reproductive biology in aquatic species, and distinct attention should be taken within the layout of breeding plans for those species. considering that 1971 AKVAFORSK, has continually performed huge scale breeding examine tasks with salmonid species, and through the newest 15 years additionally with a couple of clean water and marine species. effects from this paintings and the implications from different associations worldwide have introduced ahead enormous wisdom, which make the advance of effective breeding courses possible. The genetic development acquired in choice courses for fish and shellfish is extraordinary and masses larger than what has been completed in terrestrial livestock.

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5 and an additive genetic effect of A relative to a of +1. g. 71) (may easily be confirmed by applying the standard formulas). These parameters may be obtained from phenotypic measurements without any knowledge about the underlying allelic variation. 2 Limitations of the single gene model A single gene may only generate a limited number of genetic effects on a phenotypic trait, depending on the number of different allelic forms that the gene may occur in. 35 T. ), Selection and Breeding Programs in Aquaculture, 35–43.

Hence, for any population not already in equilibrium, linkage between the loci will delay the attainment of equilibrium. This is referred to as linkage disequilibria. Many generations of random mating may be required before equilibrium is attained, with more generations of mating required for more closely linked loci (as the chance of recombination between the two loci is lower). Tests for Hardy Weinberg equilibrium are frequently used in population studies to test for random mating and for the presence of factors altering the allele frequencies.

7 Genetic drift Genetic drift is the random fluctuation in allele frequencies, which results from the sampling of alleles during breeding in small populations. The smaller the population, the greater this sampling effect will be. An extreme example is two parents both with heterozygous genotypes. If they only produce two offspring, there is a 25% chance both will be the AA genotype, and the a allele will be lost from the population. The process of genetic drift is important where the number of breeding individuals is in the tens or hundreds.

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