I thought I had understood the difference between the 2 terms but I am afraid I still need a clear explanation. Is the following correct?
- Exon: A sequence which remains present in a mature RNA.
- CDS: A sequence which remains present in a mature RNA and codes for a protein (i.e. gets translated).
Based on these definitions, I would expect that CDS are necessarily included in exons. Now in the UCSC online page for "Get Genomic Sequence Near Gene", I have the following (exclusive) displaying choice:
- Exons in upper case, everything else in lower case
- CDS in upper case, UTR in lower case
I would therefore expect that when I select option 2, there are less nucleotides in upper case than in option 1.
But if I compare the results for the 2 options on the same sequence, I observe the following:
- A) Entire sequences in upper case in option 1 become lower case in option 2
- B) Entire sequences in lower case in option 1 become upper case in option 2
I can understand A (part of the exons which are UTR and thus non-coding become lower case in option 2), but I don't understand at all why B also happens.
Thanks for your help.