Final answer:
To obtain accurate results when an unknown DNA band size is outside the range of the DNA size ladder, extending the standard curve or running the gel with a standard that includes smaller bands should be considered.
Step-by-step explanation:
When measuring the band size of your unknown DNA sample and you find that your band has traveled further than all the bands from the DNA size ladder, then to obtain accurate results, you should extend the standard curve. Extending the standard curve involves plotting additional points that correspond to smaller DNA fragments, allowing for better estimation of the size of the unknown DNA fragment. If extending the standard curve is not possible, an alternative could be running the gel again with a standard that includes smaller bands, which could provide a more accurate measurement range for the unknown sample.
If your band has traveled further than all of the bands from the standard when measuring the band size of your unknown, you must run the gel again with a standard that has smaller bands to obtain accurate results.