Now, the vertebrate mitochondrial code has obviously evolved from the "universal" code. Imagine two codes that have evolved independently. Will a gene that belongs to one code look different than a random sequence of nucleotides to the other code?
Not necessarily. The genetic code could be not totally random - see for example de stereochemical hypothesis of genetic code origin: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1606513&dopt=Abstract
Though the genetic code variations show us that the genetic code could evolve - so a stereochemical affinity would not be the only factor behind universal genetic code origin.
[]s,
Roberto Takata