Sure, here's an example of a DNA sandbox game implemented as a single HTML file using JavaScript:
This HTML file creates a DNA sandbox game where the user can add DNA symbols by tapping on the canvas. The game displays a 10x10 grid of DNA symbols and allows the user to add symbols to the DNA strand by tapping on the corresponding symbol. The DNA strand is then redrawn on the canvas to reflect the changes.
Please note that this is a basic example and can be expanded upon to include additional features and gameplay mechanics.