Fantastic! That is exactly the kind of thing that I was thinking of but I have no knowledge of DNA so mine was rubbish.
And to keep that rhyme simple, the visual images could be of people:
in the great big person - You can have a person standing there
there was a teeny tiny cell - You zoom into the person and there's another person (smaller obviously)
in the teeny tiny cell, there were twenty three pairs of teeny tiny chromosomes - Zoom into the cell person and there are twenty three pairs of more people!
in the twenty three pairs of teeny tiny chromosomes, there was a teeny tiny gene - Zoom in to a very small person
in the teeny tiny gene, there were reeally long strands of dna! - You can have very tall person lying down (possibly being stretched!)
I think it could work, but you'd need ALOT of different people.