Task: Question Answering
Input (English): Question: A neutral gene mutation: 
 Options:  <1> Change a coding codon by another synonym without altering the amino acid sequence of the protein. <2> A coding codon changes with a different one and the protein is functionally different. <3> It generates a non-functional protein. <4> It changes the amino acid sequence of the protein without altering its function. <5> Suppresses the effect of a previous mutation.
Output (English): 4