International Journal of Molecular Evolution and Biodiversity, 2025, Vol.15, No.2, 73-83 http://ecoevopublisher.com/index.php/ijmeb 77 4 Geographic distribution pattern and genetic variation of sorghum germplasm 4.1 Overview of genetic diversity across continents The staple food of millions of people does not necessarily mean that its genetic background is singular. The genetic diversity of sorghum varies significantly between different continents. These differences do not only exist in modern times, but have gradually formed since the initial domestication stage, after long-term adaptation to different climatic conditions. In Africa, the birthplace of sorghum, this diversity is most prominent. For example, Ethiopia has diverse ecological types, and various types of sorghum have evolved here, forming significant regional differences (Enyew et al., 2022). In Niger, research has also found that sorghum in the west of the country has more abundant genetic variations than in the east. Not only that, there are multiple sorghum "races" coexisting on the African continent, such as the Guinea type, Caudium type, and Durra type, and the hybridization and interweaving between these types also make the genetic lineage more complex. The situation in Asia is different. During the process of sorghum being introduced from Africa to Asia, although it carried some primitive genes, over time and with the intervention of human selection, some gene diversity decreased, while others evolved into new alleles under new ecological pressures (Figueiredo et al., 2008). This also indicates that migration itself is a form of genetic remodeling (Tao et al., 2021). 4.2 Influence of domestication on genetic diversity When humans began to grow sorghum, its genetic composition changed. This process exists in the domestication of most crops and is often accompanied by a decrease in genetic diversity. Studies have found that cultivated sorghum has fewer DNA variants than wild types. For example, DNA polymorphism decreased by about 30% and gene activity levels decreased by about 18%. These data suggest that sorghum experienced a “genetic bottleneck” effect when it was domesticated into a cultivated crop (Casa et al., 2005). Still, traditional types-called landraces-kept about 86% of the diversity seen in wild sorghum. So not everything was lost. Although sorghum lost some of its genetic diversity during domestication, agricultural cultivation has also led to the selection of some useful traits. Traits such as plant shape, seed size, seed dormancy, and the ease with which seeds fall off have been gradually optimized to meet the needs of agricultural production. The domestication process also changed the expression pattern of genes, causing some genes to be activated or silenced. Today, cultivated sorghum and wild sorghum show significant differences in gene expression levels (Burgarella et al., 2021). 4.3 Genetic drift and gene flow in sorghum populations Sorghum’s genetic makeup is also shaped by drift and gene flow. Gene flow happens when wild and farmed sorghum grow near each other and cross. This happens a lot in places like sub-Saharan Africa. Wild, weedy, and farmed sorghum there often mix genes. In West Africa, for example, wild and weedy types often have genes from farmed sorghum. This creates a mixed genetic picture (Sagnard et al., 2011). Genetic drift is different. It’s a random change in genes, more common in small groups. Drift can make some genes disappear over time. In places like Ethiopia and Niger, drift-along with limited seed sharing between farmers—helps explain the differences between local sorghum types (Deu et al., 2008). Knowing how both drift and gene flow work is important. It helps us protect and use sorghum’s genetic resources better. 5 Case Study: Genetic Diversity of African Sorghum 5.1 Background and importance of African sorghum Sorghum (Sorghum bicolor L. Moench) is a major grain in Africa. It feeds millions of people in dry areas. It is especially important in West, East, and Southern Africa, where it grows well in many different climates and farming systems. Its genetic variety makes it a great resource for breeding. In West Africa, different local cultures and environments have helped create many types of sorghum (Faye et al., 2021). In Southern Africa, scientists also found big differences between samples. These can help create better plants in the future (Motlhaodi et al., 2016).
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