Chromosome Structure and Organization

We've all seen pictures of chromosomes, and we know that they contain DNA. But how do we get from the double helix of DNA to the X-looking shape of a chromosome? Is it just DNA, or are there other things in there? How much DNA is in each chromosome? Chromosomal structure is incredibly complicated, but now that we've learned about DNA and proteins, as well as Mendelian genetics for a little context, we are finally ready to get a more sophisticated view of what's inside a chromosome.