Gene splicing in the process of removing the introns from the RNA transcript. This is considered a post transcription modification. The exons are the portions of the transcript that will be translated into a working protein. Exons can be spliced in alternative variations. This means that one gene can result in multiple proteins.
For example if a gene contains 3 exons that gene could produce several combinations of proteins depending upon the order of splicing
variation 1 - 1-2-3
variation 2 - 3-2-1
variation 3 - 1-3-2
variation 4 - 2-3-1
This makes the one gene----->one protein model much more complicated and ultimately false.