NewSpiderman

I'm having a hard time finding any details regarding the differences between the genetic code within the nucleus and the mitochondria. There are some differences in the pairing of amino acids to codons, but does anyone know exactly why this is so? Are there different types of tRNA synthesized by each distinct genome which result in such disparities or is there another reason for these variations? Any information, especially some references, would be appreciated. Muchas gracias, peeps!