Animal Molecular Breeding, 2025, Vol.15, No.1, 9-18 http://animalscipublisher.com/index.php/amb 13 to zero or negative values, suggesting that dominant genotypes may have environmental specificity (Mourão et al., 2023). This requires that breeding strategies must take environmental adaptability into account. Nevertheless, under the same breeding conditions, the genetic consistency between body weight and growth rate is relatively high (0.65~0.99), enabling the breeding results to be effectively transformed among similar systems (Trọng et al., 2013; Turra et al., 2016; Thỏa et al., 2016; Setyawan et al., 2022). However, the genetic expression of body type characteristics is more environmentally sensitive, and differentiated breeding schemes need to be developed to adapt to different breeding scenarios (Trọng et al., 2013; Nguyen et al., 2017). 5 Genetic Regulatory Mechanism 5.1 The core regulatory role of QTL and functional genes Quantitative trait loci (QTL), insulin-like growth factor 1 (IGF1), growth hormone (GH) and other key genes have core functions in the growth regulation of tilapia. Genome-wide association analysis has identified multiple QTL regions significantly associated with body size parameters, among which some loci can explain more than 70% of the weight variations (Liu et al., 2014). Important genes in these regions, such as growth hormone receptor 2 (GHR2), significantly affect the development process by regulating the activity of the IGF-1 signaling pathway, and different GHR2 genotypes correspond to differentiated growth manifestations (Liu et al., 2014). Molecular biological studies have confirmed that the GH/IGF signaling axis and myostatin (MSTN) constitute the main growth regulatory network. High growth performance strains generally show the characteristics of high expression of GH/IGF pathway genes and low expression of MSTN, making them important targets for genetic improvement (Herkenhoff et al., 2020; Wu et al., 2022). 5.2 Breeding applications of molecular marker technology Molecular marker techniques based on single nucleotide polymorphisms (SNPS) have been widely applied in the dynamic tracking of growth traits. By constructing high-density genetic maps, researchers have identified SNP loci closely related to body type, gender and morphological characteristics, providing technical support for marker-assisted breeding (Liu et al., 2014; Wang et al., 2024). For example, the specific SNP markers of the IGF1 gene can be used as reliable genetic markers for the breeding of growth traits across populations (Table 1) (Ukenye et al., 2020). The discovery of QTL linkage sites enables the screening of fast-growing individuals at the juvenile fish stage, significantly improving the breeding efficiency of important economic traits (Liu et al., 2014; Wang et al., 2024). 5.3 Current development status of genome selection technology Although genomic selection technology (using whole-genome information to predict breeding values) has application prospects, it is still in the stage of technological improvement at present. The latest research, through genome-wide association analysis (GWAS) and transcriptome techniques, has resolved genetic pathway networks such as MAPK and VEGF that are closely related to growth adaptation (Powell et al., 2021; Wang et al., 2024). Despite the technological breakthroughs, the practical application of this method still faces challenges such as the analysis of gene-environment interaction effects and the modeling of the genetic architecture of complex traits. With the continuous expansion of the genomic database, this technology is expected to become a new accelerator for aquatic genetic improvement (Powell et al., 2021; Wang et al., 2024). 6 Genetic Improvement Technology Pathways 6.1 Family breeding and hybridization technology application Family screening and interspecific hybridization constitute the basic techniques for genetic improvement of tilapia. Family selection and breeding screen dominant families for subsequent reproduction by evaluating core indicators
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