DNA is isolated from a clinical sample. The absorbance at 260nm is 0.489, and the absorbance at 280nm is 0.257. Is this sample of sufficient quality for use in subsequent analyses?

Yes

Explanation:

A high quality DNA sample will have a 260/280 ratio of around 1.8. This value means that the DNA is sufficiently pure and free from other contaminants that could affect downstream experiments and analysis.

The ratio for this sample is 0.489/0.257 = 1.9

This is close to 1.8, and therefore the sample is of sufficient quality ot use downstream.