How can mutations be ? give 2 examples

Having two copies of the mutated genes cause sickle cell anemia, but having just one copy does not, and can actually protect against malaria - an example of how mutations are sometimes beneficial. 

The majority of mutations have neither negative nor positive effects on the organism in which they occur. These mutations are called neutral mutations. Examples include silent point mutations. They are neutral because they do not change the amino acids in the proteins they encode.

Hope this helped :)