How do you know if there is a ‘bad’ genetic mutation (by colour, shape etc)?

Question: How do you know if there is a 'bad' genetic mutation (by colour, shape etc)?
- Keywords:
  bad,
  gene,
  mutation
Asked by Emz to Gaia on 10 Mar 2016.
- Gaia Andreoletti answered on 10 Mar 2016:
  
  Hi Emz,
  Good question!
  
  I can say that a mutation is bad because there are lots of software that help me to annotate each mutation, they are really handy to distinguish good from bad mutations.

Question: How do you know if there is a 'bad' genetic mutation (by colour, shape etc)?