What type of DNA was discovered by investigating why some fruit flies have wing spots and others don’t?

Paintbrush gene switch on and off

Explanation:

The study on the Fruit fly by Sean Carroll showed that the expression of a trait is controlled by the switch which turns on and off the genes involved in the spots on the wings.

The gene which is responsible for the wing spots is known as paintbrush genes and when they are activated by the switch express the traits and when switched off do not express the trait.

Thus, in the case of wing spots in the fruit fly, the flies with spots show an expression of the paintbrush genes and without wings do not show the expression of genes.

Thus, the Paintbrush gene switches on and off is correct.