From this image
We can see several exons that are actually introns in other genes. It's not a really a different gene, it's an alternative splicing of a gene. My background is not biology so is it possible for alternative splicing to behave like this? I only know that alternative splicing is just exon skipping and introns will just stay introns and not become exons. Can someone explain this to me and give any suggestions on which part of biology (or genetics) I need to learn. Thank you.