Candidate Gene Approach Essay

Candidate gene approach: The candidate gene approach studies the relationship between the traits and known genes that may be associated with the physiological pathways underlying the trait (Liu et al., 2008). Candidate gene approach is implemented in 5 steps: (1) construction or collection of a resource population, (2) phenotyping of the specific components of the trait(s), (3) selection of genes or functional polymorphisms that potentially could affect the traits, (4) genotyping of the resource population for the selected genes or functional polymorphisms, (5) statistical analysis of the phenotypic and genotypic data (Da, 2003). This is an effective way to find the genes associated with the trait. So far a number of genes have been investigated.
Transgenic livestock and fish have been produced which contain an exogenous GH gene. The first hypertrophic pig was produced with the microinjection of chicken cSKI (Sloan–Kettering protein), resulting in individuals, showed evident hypertrophy and enlargement of the hams and shoulders (Pursel et al., 1992). A transgene consisting of the zinc-inducible metallothionein promoter driving ovine growth hormone expression, showed significant decrease in fat and increase in muscle tissue (Pursel et al., 1997). Saeki et al. (2004) developed transgenic pigs carrying unsaturated fatty acid genes, originally from linoleic and linolenic acids that are essential for mammalian nutrition and regulate many biological processes, including the growth of piglets. Transgenic pigs showed 3 fold higher levels of n-3 fatty acids and 23% lower level n-6 fatty acids then non transgenic pigs. Humans can’t produce these fatty acids, nor can livestock animals. The tissues of livestock animals contain high level of omega 6 fatty acid but livestock lack the enzymes (n-3 fatty acid de-saturase) to convert omega 6 fatty acids to omega 3 fatty acids. The fat-1 gene desaturase found in the roundworm C. elegans convert omega 6 fatty acids to omega 3 fatty acids by introducing double bond into the gene (Saeki et al., 2004). Phytase transgenic pigs have been developed to address the problem
The growth-enhanced trait has attracted great interest as it could be an answer for increasing the yield of fish farms in addressing the need for greater availability of high quality protein, whilst at the same time overcoming environmental concerns. In fish, dramatic increases have been shown in growth rate of transgenic Atlantic salmon using the gene promoter and growth hormone gene derived from fish species. A salmon modified to grow four to six times faster than conventional salmon. It contains an additional salmon growth hormone gene and an anti-freeze gene from an ocean pout (Macrozoarces americanus) fish which will allow it to produce growth hormone all year-round rather than just in the warm months like conventional salmon. (Du et al., 1992; Devlin et al., 1994). In addition, the production of these growth-enhanced salmon will have vast positive environmental