A single germline mutation can have a range of effects:

1. No effect or neutral effect

   

   Some mutations don’t have any noticeable effect on the organism. This can happen in many situations: perhaps the mutation occurs in a stretch of DNA with no function, or perhaps the mutation occurs in a protein-coding region, but does not affect the amino acid sequence of the protein. Other mutations have a noticeable effect, but one that doesn’t seem to help or hurt.  For example, a single mutation caused this cat’s ears to curl backwards slightly, a trait that doesn’t seem to affect its health.

2. Detrimental effect

   Some mutations harm an organism’s ability to survive and reproduce. For example, in humans, Marfan syndrome is caused by a mutation affecting a protein that forms part of connective tissue, leading to heart problems and other health challenges. Detrimental mutations known as lethals disrupt DNA critical to survival and cause the death of the organism.

3. Beneficial effect
   Other mutations are helpful to the organisms that carry them. For example, DDT resistance in insects is sometimes caused by a single mutation. While resistant insects might be downer for us, they are undoubtedly helpful for bugs trying to survive on pesticide-laden crops.

According to popular culture, it seems that mutations mainly cause either cancer or superpowers. Of course, the cancer is true enough. But in the real world, beneficial mutations are rare. Most mutations have no effect or a detrimental effect. And major evolutionary change (e.g., the “superpower” of flight in bats!) generally involves the accumulation of many, many mutations over many, many generations.