International Journal of Molecular Zoology, 2025, Vol.15, No.2, 90-100 http://animalscipublisher.com/index.php/ijmz 95 Genomic selection goes a step further, using the high-density marker information of the entire genome to establish a predictive model and directly estimate the breeding value for young candidate individuals. Many international breeding companies have applied GS to the purebred selection of chickens. For instance, after a certain company in the Netherlands implemented GS on broilers, the feed conversion rate improved by more than 50% per generation. It has been reported that by introducing homozygous and heterozygous effect parameters in genomic selection, the phenotypes of the offspring of hybridization between two strains can be predicted to a certain extent, and thus be used to select the best parental combination (Wu and Zhao, 2021). Furthermore, for specific simple genetic traits (such as the slow feather gene used to distinguish male and female chicks), it is an example of directly using molecular markers to control the hybridization effect (de Haas et al., 2021). By editing genes related to muscle growth inhibition, it is expected to breed patrilineal varieties with higher muscle yield (Nawaz et al., 2025). Although the application of gene editing in poultry is still in the experimental stage, its potential is huge: A comparison between L-B hybridization and L-purebred schemes. Simulation studies show that in the breeding of dual-performance chickens, the introduction of gene editing can increase genetic improvement progress by up to 81% and accelerate the simultaneous improvement of the negatively correlated traits of meat production and egg production (Figure 2) (Chuang et al., 2024). Figure 2 Breeding scheme for the two scenarios considered, L-B cross and L-Pure. For each scenario, breeding with and without gene editing were simulated (Adopted from Chuang et al., 2024) 5 The Improvement Path of Egg Production Performance by Hybridization 5.1 Hybridization application of special lines for laying hens In the breeding of laying hens, hybridization technology also plays an important role. Modern high-yielding laying hens are basically commercial hybrid chickens obtained by crossing multiple specialized strains. A well-known case is the Hy-Line laying chicken line, which is a crossbreeding of four grandparent lines. Among them, two paternal lines are responsible for giving the offspring larger body size and stronger vitality, while two maternal lines provide high-yield egg genes and firm eggshell quality (Ramteke et al., 2025). Almost all commercial egg-laying chicken production uses hybrid chickens to fully utilize the hybrid advantage. At present, there are mainly two types of hybridization: two-line hybridization and three-line hybridization. White-shelled laying hens are mostly two-line hybridization, such as Bai Lai Hang Pure Line A× Bai Lai Hang Pure Line B. Most brown-shelled laying hens are three-line hybrids. For instance, the paternal line is derived from Luo Dao Hong × Bai Luo Ke and then crossbred with the maternal line Lai Hang. The establishment of these supporting
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