Yeegg

Breeding Programmes

FAMILY SELECTION

The BGCL nucleus population of more than 300 families of Atlantic Salmon produces large numbers of individuals for testing and selection.

By comparing families for different traits important in commercial production, we are able to accurately identify those families which have genetic advantages. Family selection is especially important in traits which are difficult to measure on individuals — such as disease or parasite resistance — or are destructively measured, such as fillet yield or colour.

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Individual selection

In traits such as growth, where the phenotypes are easily measured on breeding candidates, individuals can be efficiently selected based on their own performance.

In recent years new genomic methods have been developed to identify individuals for breeding based on their DNA sequence by genotyping. By understanding which genotypes (often using SNPs — single nucleotide polymorphisms) are associated with good performance in each trait, it is possible to screen populations to find individuals whose offspring will perform best. Where a large number of SNPs are used on each individual, this is known as Genomic Selection. In some traits, where single SNPs are associated with a large amount of variation (often described as QTLs — quantitative trait loci), individuals can be selected on a small number of SNPs. In both of these cases, genotyping has improved the effectiveness of selection by more accurately identifying the individuals with improved performance. This is particularly important in traits such as disease and parasite resistance and harvest yield and quality.

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QTL-QUANTITATIVE TRAIT LOCI

A QTL is a position on the genetic sequence (genome) associated with a significant amount of variation of a trait, often identified using one or a small number of SNPs.

The QTL suggests that a major gene is located close to that position on the genome. The SNPs are genetic markers for the QTL and can be used in a special form of selection known as marker-assisted selection (MAS).

In Atlantic Salmon, a major QTL has been identified for resistance to IPN virus which accounts for over 80% of the genetic variation in resistance. SNP markers for this QTL have been used to identify and breed from resistant individuals in the nucleus and for commercial egg production, reducing the number of outbreaks of IPN. Research work continues to identify major QTLs for other traits. Although in most traits the majority of variation is accounted for by many genes where Genomic Selection is more effective.

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GENOMIC SELECTION

Marker-assisted selection for major QTLs is a very effective method for traits where a major gene accounts for the majority of genetic variation. In most traits, however, genetic variation is controlled by a large number of genes each with a small effect.

For these traits, Genomic Selection (GS) using a large number of SNPs is more effective in identifying individuals for breeding. BGCL use a micro-chip with over 50,000 SNPs covering the whole genome (SNP chip). Extensive R&D examining the relationship between the SNPs and traits in test populations has provided the background information for GS in the BGCL populations.

Using advanced genetic methods, we are able to successfully select parent fish with the most suitable genes for commercial egg production. Our breeding programme is internationally recognised for the offspring quality — rapid growth coupled with delayed sexual maturity, disease and parasite resistance and an outstanding flesh quality.

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