Western Blot Two Proteins - (Aug/31/2011 )

Hello Forum,

please have a look at this image

http://imageshack.us/photo/my-images/98/0bigg.jpg/

There are two proteins A and B in the right column.
Marker B is the protein´s length of healthy people.
But as you can see there are two different markers for this protein (the western Blot was made for one patient).

How can you explain the appearance of two different markers in one patient?

Can you explain with examples how changes of genes can lead to this result?

These are very much homework questions... please either post in the homework section, or at least demonstrate that you have made some attempt to answer them yourself, or preferably both!