Maize Genomics and Genetics 2024, Vol.15, No.4, 160-170 http://cropscipublisher.com/index.php/mgg 163 such as larger kernels and a more compact plant structure (Xu et al., 2019). These traits were selected over generations, leading to the maize we know today. It was found that the evolutionary history of maize also includes post-domestication adaptation to diverse environments, allowing it to spread far beyond its original habitat (Manchanda et al., 2018; Xu et al., 2020). 4.3 Population structure and gene flow The population structure of maize has been shaped by both its domestication and subsequent breeding practices. Genetic analyses have revealed distinct population structures within maize, influenced by gene flow between different maize varieties and their wild relatives. For example, Moreno-Letelier et al. (2020) found through genetic analysis of 29 wild and 43 cultivated maize populations that maize domestication was not a single event but the result of multiple gene flow and selection events (Figure 1). Multiple gene flow events between maize and its wild relatives indicate that the domestication process was long and ongoing. These findings help in conserving wild relatives to maintain genetic diversity for the future. Figure 1 Population graph depicting relationships among populations, including migrations events, obtained with TreeMix with 30 673 SNPs (Adopted from Moreno-Letelier et al., 2020) Image caption: The figure reveals migration events and genetic drift among different populations; The branch lengths in the figure are proportional to the degree of genetic drift, and migration events are shown through high deviations in the covariance matrix; The results indicate migration events from a highland mexicana population to maize, from maize to another highland mexicana population, from lowland Jalisco toZ. luxurians, and from maize to a parviglumis population; These findings suggest the existence of complex gene flow during the domestication of maize (Adapted from Moreno-Letelier et al., 2020) 4.4 Selection pressures and adaptation Selection pressures during maize domestication and subsequent adaptation to new environments have been a major focus of genomic research. The identification of genomic signatures of selection has provided insights into the adaptive traits that were favored during domestication. For instance, the study of DNA methylation has highlighted the role of epigenetic modifications in maize adaptation, with certain DMRs acting as cis-acting elements that modulate gene regulation (Xu et al., 2020). These findings suggest that both genetic and epigenetic factors have played a role in the adaptation of maize to various environmental conditions, contributing to its widespread cultivation and success as a crop (Manchanda et al., 2018; Xu et al., 2020).
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