International Journal of Molecular Zoology, 2025, Vol.15, No.1, 20-28 http://animalscipublisher.com/index.php/ijmz 24 a result, white feathers or lighter color would occur (Yang et al., 2022; 2024), protein and mRNA expression analyses also support this finding. Xu et al. (2022) found that the expression of TYRP1 was higher in female geese, while ASIP was more active in male geese, which also matched the depth of their feather color. Some tissue staining experiments, including staining specifically targeting melanin, clearly demonstrated the distribution changes of melanin in feathers, proving that these gene mutations do affect feather color (Xu et al., 2022; Yang et al., 2024). 5 Functional Genomics and Gene Editing 5.1 CRISPR/Cas applications in poultry The CRISPR/Cas gene editing technology enables researchers to precisely manipulate and study the key genes that affect feather color (Lin, 2024). Zhou et al. (2024) indicates that although there are currently few studies on the application of this technology in domestic geese, with the continuous improvement of genome sequencing and annotation, for instance, the chromosomal genome of the Hungarian white goose has been assembled. These efforts have laid a solid foundation for future gene editing research. Genes such as KIT, EDNRB2 andTYRP1 have been confirmed to be closely related to feather color changes, providing a clear research direction for functional verification and mutation analysis using CRISPR/Cas technology (Ren et al., 2021; Wen et al., 2021; Yang et al., 2022; Wen et al., 2023; Yang et al., 2024). 5.2 Overexpression and knockdown models Researchers found through transcriptome analysis that genes such as EDNRB2, MLANA and TYRP1 were expressed at different levels in geese with different feather colors. This indicates that their functions can be understood by regulating the expression of these genes (Xu et al., 2022; Yang et al., 2022; Wen et al., 2023; Yang et al., 2024). If the expressions of EDNRB2 and MLANAare reduced, melanocytes will decrease, thereby forming white feather patches. The higher the expression of TYRP1 is, the darker the color of the feather will be (Xu et al., 2022; Yang et al., 2022; 2024). 5.3 Challenges in applying functional genomics to geese Compared with chickens, geese still lack mature transgenic and gene editing systems, making it difficult to verify many candidate genes in experiments (Sello et al., 2019; Zhou et al., 2024). Feather color is not determined by a single gene. Usually, multiple genes and regulatory elements act together, and the genetic structure is very complex, making it more difficult to explain in research (Ren et al., 2021; Yang et al., 2022; 2024). The gene expression patterns and signaling pathways among different goose breeds are also different, meaning that the research results from one breed may not be suitable for application to other breeds (Sello et al., 2019). There are still some practical problems. For instance, genetically modified geese can trigger ethical controversies and pose considerable technical difficulties, which have restricted the progress of research. 6 Genome-Wide and Transcriptomic Approaches 6.1 Whole genome resequencing and GWAS Studies have identified multiple important genetic loci through population resequencing and genome-wide association studies (GWAS). Wen et al. (2021) suggested that an 18-base deletion mutation in the KIT gene has a strong relationship with the white feather characteristics of Chinese domestic geese. In the same year, Ren et al. (2021) also discovered some other candidate genes through whole-genome scans, such as KITLG, MITF and TYRO3, which may regulate the expression of feather color through selection differences between white-feathered and grey-feathered goose flocks. In Huoyan geese, selective clearance analysis revealed that TYRP1 is a potential key gene affecting the feather color of young geese, enriching the understanding of genes related to feather color (Wen et al., 2023). Yang et al. (2022) also discovered specific mutations and expression differences of EDNRB2 and MLANA in the comparative genomic study of graylag and swan geese, all of which are related to the phenotype of feather color. 6.2 RNA-seq analysis of feather follicles The feather sacs in the embryonic skin of Anser anser and Anser cygnoides were compared, and tens of thousands of unigene and differentially expressed genes (DEGs) were identified. Sello et al. (2019) found through functional
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