They are located by spliceosomes and those genes possessing them are termed "split."  
In 1995 scientists at Ohio State discovered that they possess a property called "homing."  Theories of how they arose are divided into the "late" and "early" camps and could not be resolved when they were discovered in the cyanobacterium Fischerella.  They can occur in the middle of a domain, and sometimes even within a single codon.  They are located by spliceosomes and those genes possessing them are termed "split."  FTP, name these pieces of DNA that are excised as opposed to exons.
In 1995 scientists at Ohio State discovered that they possess a property called "homing."  
introns