Animal Molecular Breeding, 2025, Vol.15, No.1, 19-28 http://animalscipublisher.com/index.php/amb 24 Anser anser. This genetic diversity is of great significance for the conservation and improvement of goose breeds, as it is helpful for preserving the genetic differences within the breeds. The genetic basis of European domestic geese is relatively narrow, and many individuals have very similar haplotypes, indicating that during their domestication process, they may have experienced a genetic bottleneck or the founder effect. Ancient DNA studies have found that the genetic differences among early domestic goose populations were more obvious, while in modern domestic geese, due to long-term directed breeding and genetic drift, the genetic diversity has gradually decreased (Heikkinen et al., 2015; Honka et al., 2018; Jing et al., 2022). 6.2 Detection of selection sweeps and differentiated regions Analysis of selection signals in Central European domestic geese revealed that genomic regions related to functions such as the nervous system, immunity, metabolism, vision, bone development, and blood oxygen transport have been strongly artificially selected. In Chinese geese, the 14-base insertion mutations of the EDNRB2 gene are closely related to the characteristics of white feathers. The two SNPS within the EXT1 gene are related to the unique frontal tumor structure of Chinese geese. CSMD1 and LHCGRare respectively related to the brooding behavior of Central European domestic geese. The candidate genes TGFBR3L, CMYA5, FOXD1, ARHGEF28 and SUCLG2 are closely related to the growth rate, reproductive ability and reproductive performance of geese (Jing et al., 2022; Chen et al., 2023; Zhang et al., 2023). 6.3 Population structure and admixture Most Chinese goose breeds can be traced back to a common ancestor, but some breeds like the Yili goose show signs of genetic hybridization with other Chinese geese. The origin of European domestic geese is more complex. Genetic components from Chinese swan goose (Anser cygnoides) have also been found in some European breeds, indicating that gene flow occurred in history. The two-way gene exchange and frequent hybridization between wild geese and domestic geese are also ongoing. These factors together have shaped the complex genetic pattern of modern geese. The study confirmed through cluster analysis and demographic models that there was continuous gene exchange in the modern domestic goose population and presented a "Mosaic ancestral structure" (Ottenburghs et al., 2017; Chen et al., 2023; Zhang et al., 2023). 7 Mitochondrial and Nuclear Genome Perspectives 7.1 Maternal lineage tracing using mtDNA Heikkinen et al. (2015) and Qi et al. (2024) analyzed the mitochondrial control regions and cytochrome b (CYTB) genes of wild geese and domestic geese and found that the mtDNA diversity of European domestic geese was relatively low, with most individuals having only a few haplotypes that were very close to each other, indicating that their maternal genetic sources were relatively single. Qi et al. (2024) also found that Chinese domestic geese exhibit higher haplotype diversity and a more complex population structure. Some breeds also have frequent gene exchanges, suggesting that Chinese geese may have multiple maternal origins. These findings support the view that Chinese geese originated from swan goose (Anser cygnoides), while European geese originated from greylag goose (Anser anser) (Ren et al., 2016). 7.2 Discordance between mtDNA and nuclear genomes Chen et al. (2023) demonstrated that although mtDNA can provide clear maternal genetic information, nuclear genome studies have shown that there is significant gene exchange and genetic mixing between domestic geese in China and Europe, as well as between domestic geese and wild geese. Ren et al. (2016) and Zhang et al. (2023) both hold that Yili geese cluster with European geese on the mtDNA phylogenetic tree, which may indicate that there was once genetic infiltration between them or that they shared an ancient haplotype. Further analysis of the nuclear genome also found that during the domestication process of geese, selection was mainly concentrated on genes related to growth, reproduction, immunity and morphological traits, and these characteristics were also continuously affected by genetic mixing events.
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