Science can associate one feature with one gene: skin color (what's you probably focus on if you're American), digestion of milk, response to some medicines, predisposition to some diseases, etc.
Some are naked eye observable (skin color), others need medical investigations.
Admitting that is not called racist and in some case knowing it can be vital.
Racism is when you assign a social class to some features (skin color in the US).
This being said, science can spot the gene responsible for an elementary feature, but since we are all a mosaic of hundreds of features, science is unable to define subgroups of humans, not even to draw boundaries between groups.