Mobile genetic elements 10–200 kb in size that have become integrated and fixed. They are found in many bacteria where they may code for a range of functions, e.g. the multidrug-resistance phenotype in Salmonella that depends upon an antibiotic resistance gene cluster in a 43-kb genomic island named salmonella genomic island 1 (SGI1). They allow the rapid spread of a trait between phylogenetically distinct organisms. Islands often have an atypical G+C content, are frequently associated with tRNA-encoding genes and tend to be flanked by repeat structures.
Subjects: Medicine and Health.