I was working with the refseq genes hg19 file to define genomic regions and I downloaded 4 files from the UCSC table browser
1. with all exons
2. 5'UTR exons
3. 3'UTR exons
4 Coding exons
I realised that the no. of records in 2+3+4 are more than that in 1. It doesnt strike me at the moment, why should this be the case. Shouldn't 5 UTR+3UTR+Coding exons add up to total no. of exons in the genome ? Or am I missing something obvious ?