The genetic system does not consist of DNA alone. Enzymes must read the DNA code; mRNA will be produced from that reading. The mRNA will take that code to ribosomes and bond to them for production. Carrier RNA will transport the amino acids to be used in production to the ribosome. And countless other highly complex enzymes that will permit intermediate processes to be carried out must all be present.
In addition, such an environment can only be one like the cell, in which all the raw materials and energy sources are present, and which is completely isolated and controlled. (See DNA, Ribosomes;RNA World Thesis, the.)