Genes aren't one unbroken stretch of DNA — this discovery rewrote molecular biology
In 1977, Phillip Sharp and Richard Roberts independently found that genes in complex organisms are broken into coding pieces (exons) interrupted by non-coding stretches (introns), which the cell splices out before making protein. It overturned the bacteria-derived assumption that a gene is one continuous sequence. The 'split gene' discovery won them the 1993 Nobel Prize.