Triticeae Genomics and Genetics, 2024, Vol.15, No.1, 56-65 http://cropscipublisher.com/index.php/tgg 58 significantly lower in domesticated barley compared to its wild counterpart (Kilian et al., 2006). This reduction in diversity is attributed to bottlenecks during domestication and subsequent breeding processes (Kilian et al., 2006). Additionally, structural variations such as copy number variations (CNVs) have been observed, with higher levels of CNV diversity present in wild barley compared to cultivated forms (Muñoz‐Amatriaín et al., 2013). These CNVs are often associated with genes involved in disease resistance and other agronomically important traits (Muñoz‐Amatriaín et al., 2013). Figure 1 Signatures of positive selection in barley differentiated by chromosome and zone (Adopted from Chen et al., 2022) Image caption: (a) Selective sweep signal (μ) of barley genomes. Red colours represent genomic regions with μ values above the 95th percentile. The top track shows the chromosome diagrams, with the gradient of blue colours representing zone 1 (light blue), zone 2 (medium blue) and zone 3 (dark blue) regions, and the red bars representing the centromere; (b) Distribution of μ values by chromosome for different barley groups; (c) μ values by zone (data from all seven chromosomes combined) for different barley groups (Adopted from Chen et al., 2022) The domestication process also involved changes in specific genes that contributed to the agronomic traits selected by early farmers. For example, the HvWAK1 gene, which is involved in root proliferation, showed reduced sequence diversity in domesticated barley, suggesting selection for particular cis-regulatory variants that may have indirectly influenced seed size through increased plant vigor (Czajkowska et al., 2019). Furthermore, the evolution of the grain dispersal system in barley involved mutations in two adjacent genes that converted the brittle rachis of wild barley into a tough, non-brittle form, facilitating effective harvesting (Pourkheirandish et al., 2015). 2 Nucleotide Diversity and Research Methods 2.1 Nucleotide diversity and measurement Nucleotide diversity is a measure of genetic variation within a population. It quantifies the degree of polymorphism at the nucleotide level, providing insights into the genetic health, evolutionary history, and adaptive potential of a species. Nucleotide diversity is typically represented by the symbol π (pi) and is calculated as the average number of nucleotide differences per site between any two DNA sequences chosen randomly from the population.
RkJQdWJsaXNoZXIy MjQ4ODYzNQ==