‘Strong’ genes are called dominant and require just one copy of themselves to have an effect. Recessive genes need two copies to exert their influence (ie you need to have inherited a copy from both your parents).
Dark eyes are a dominant trait as it only takes one copy of the relevant gene to stimulate the eye to produce melanin – the pigment that colours eyes brown. Blue eyes, on the other hand, are recessive as the presence of melanin masks the blue colour – somebody with one gene for blue eyes and one for brown eyes will have brown eyes.
This is just one of the many ways in which dominant and recessive genes interact, but there’s still a lot more for scientists to learn about how they work.
Answered by Alexandra Cheung