International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.1, 44-53 http://ecoevopublisher.com/index.php/ijmec 45 chickens. We collated data from different regions, hoping to gain a clearer understanding of how chickens adapt to different living environments through their genes, and to provide some ideas for improving the adaptability and production capacity of chickens in the future. 2 Global Patterns of Chicken Genetic Diversity 2.1 Regional genomic variation and structure Chickens around the world have rich genetic diversity and a relatively complex population structure. These changes are the result of natural environmental selection on the one hand, and are also related to human breeding selection on the other. Scientists have conducted whole-genome analysis of chickens from China, Africa, Europe and Asia, and found that there are obvious genetic differences between chicken breeds in different regions. Chickens in many places have their own unique genetic changes, which are closely related to the environment in which they live (Hu et al., 2025). For example, in chickens adapted to high altitudes, droughts, tropical or cold regions, researchers have found genes related to energy metabolism, ion channels, and stress responses (Shi et al., 2022). After analyzing a large amount of SNP data, people have also found that chicken breeds on different continents have a complex genetic history of mixing and differentiation (Dementieva et al., 2024). 2.2 Influence of human-mediated selection In fact, many of the genetic changes in chickens are man-made. In order to make chickens more in line with human requirements, such as growing faster, laying more eggs, and having beautiful feather colors, or even just to cater to the market's preference for skin color, people have long begun to select and breed from generation to generation. The genes in some areas, especially the gene loci related to traits, and even the sex chromosomes, clearly show the "traces" of these selections (Li et al., 2019). However, not all chicken selections are for economic benefits. Some chicken breeds are actually preserved to adapt to the local environment. For example, tropical chickens are more heat-resistant, while northern chickens are more cold-resistant. However, this kind of artificial selection also has side effects, especially in large-scale commercial breeding. In order to maintain the desired characteristics, the genetic diversity of many breeds has been compressed a lot, sometimes even to the point of inbreeding. In contrast, this situation is less common in local chicken breeds (Fleming et al., 2017; Bai et al., 2024). 2.3 Contributions of indigenous and local breeds Local and indigenous chicken breeds are critical in maintaining genetic diversity. They have evolved over a long period of time in complex local environments, so they have strong adaptability, such as being able to withstand high temperatures, drought, and certain diseases (Zhang et al., 2024). Genomic studies of chickens in Africa, Asia and other places have found that these local breeds often contain special genes related to stress response, immune function and metabolic capacity. These genes are rare in commercial chickens (Fleming et al., 2016). These genetic characteristics make local chickens particularly valuable in sustainable farming. If we have to face the challenges brought by climate change in the future, these breeds may play a big role in breeding (Gheyas et al., 2020). 3 Genomic Signatures of Environmental Adaptation 3.1 High-altitude adaptation Chickens living on the plateau, such as Tibetan chickens, have some special genes that help them adapt to the thin air at high altitudes. Studies have found that some of the parts of these chickens' genes related to calcium signals have changed, which may be related to their ability to cope with hypoxia (Wang et al., 2015). In addition, local chickens in Africa have similar situations. Some areas in their genomes have been found to be related to high altitude stress, such as hypoxia and susceptibility to blood clots. This shows that whether chickens can adapt to the plateau has a lot to do with some specific genes (Gheyas et al., 2020). 3.2 Heat and cold stress tolerance Chickens in tropical and cold regions also have their own genetic adaptability. Some genes of chickens living in the tropics, such as TSHR, HSF1 and SLC33A1, have undergone significant changes, which may help them better regulate body temperature and metabolism (Figure 1) (Rachman et al., 2024). For chickens living in cold places,
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