Low-amylose barley cultivars have less amylose in their grains compared to normal barley. The reason for this is a mutation in a gene called GBSSI, which is responsible for making amylose. This mutation causes a delay in amylose production during grain development. The mutation leads to a deletion in the gene's promoter region, affecting how much GBSSI is produced in the endosperm of the grain. All low-amylose cultivars share this same mutation, suggesting a common ancestor. Some barley cultivars have no amylose at all due to different mutations in the GBSSI gene. These findings help explain why some barley varieties have different levels of amylose in their grains.