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title: "7.4 Breeding aspects of genes with large (positive) effects (2024)"
canonical: "https://wiki.groenkennisnet.nl/space/TAB/296681536/7.4%20Breeding%20aspects%20of%20genes%20with%20large%20(positive)%20effects%20(2024)"
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Molecular genetic research increases the number of genes with marked effect (major genes) on the quality of animal’s products and affect fertility in several species.

## **Double muscling gene**

![IMG_3659-20150530-121746 (1).jpg](media://1ed911d4-bf08-4593-8196-b76341a2a53d)

 For example, in many species (e.g. cattle, sheep, pigs, horses, dogs and humans) the myostatin gene is known. This locus has a recessive allele that in homozygous animals gives rise to the double muscle pattern. A breed where the fixation of this allele is aimed at is the Belgian White Blue cattle breed. The breed is famous for the heavy carcasses, the thick muscles and the high percentage of meat in the carcass. However, a high percentage of the females that are homozygous for the double muscle allele of the myostatin gene cannot give birth in a natural way. Those calves are born through caesarean section, leading to a severe ethical discussion in many countries. In other species the animals homozygous for the myostatin gene give similar problems when they give births and caesarean sections are required.

## **Milk protein genes**

Another example of a gene with a known major effect occurs in dairy cattle. In dairy cattle a number of milk protein genes are known from which the alleles have a different effect on cheese yield. For example, beta-lactoglobulin alleles (gene located at chromosome 11) have a marked effect on the efficiency of cheese production.  Cows with the BB-genotype are the favorite ones for cheese makers. A better coagulation lead to a 10 per cent higher cheese yield. The EE-genotype has a strong negative on the coagulation. Therefore dairy bulls are tested for this milk protein. The DGAT1 alleles (gene located at chromosome 14) influence fat percentage in milk and the milk fat composition. The K-allele increases fat and protein percentage and fat yield, while it decreases milk and protein yield. And very importantly, the milk fat composition from cows with K-alleles is different: they produce more fatty acids that are considered to be less favourable for human health.  

## **Meat quality gene**

In pigs the halothane gene (located at chromosome 6) is known to influence the stress susceptibility and the meat quality. Androstenone is responsible for (an awful) boar taint in the meat of intact boars. Usually boars are castrated to avoid this boar taint in their meat, but selecting against boar taint is a better approach that makes castration of the boars redundant.

## **Fertility genes**

In sheep several genes are described that have an influence on the litter size. An example is the Booroola gene present in the Australian Merino that has a marked effect: the heterozygous carrier produces one lamb more and the homozygous carrier two lambs more per litter. This allele is now also present in the Dutch Texel breed by crossbreeding merino rams carrying the Booroola allele with Texel ewes and backcrossing the crossbreds with Texel sheep.

## **Color genes**

In all species a lot of attention is paid to the inheritance of the color of the coat. The color of the coat is an important trait in the recognition of breeds. Breed associations often have strict rules for the required color pattern. In companion animals and animals used for leisure purposes, breeders pay a lot of attention to the inheritance of color and breed for special phenotypes. In the past, many genes and alleles are described that are involved in the color inheritance. First, we start to describe a few genes that play a role in coat color in ruminants and then we mention per species additional particulars.  


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