Mutations

Here is your template DNA strand:
CTT  TTA TAG TAG ATA CCA CAA AGG

Write out the complementary mRNA that matches the DNA above.
Write the anticodons and the amino acid sequence.
Change the nucleotide in position #15 to C.
What type of mutation is this?
Repeat steps 1 & 2.
How has this change affected the amino acid sequence?
Now remove nucleotides 13 through 15.
Repeat steps 1 & 2.
What type of mutation is this?
Do all mutations result in a change in the amino acid sequence?
Are all mutations considered bad?
The above sequence codes for a genetic disorder called cystic fibrosis (CF).
When A is changed to G in position #15, the person does not have CF.  When T is changed to C in position #14, the person has the disorder.  How could this have originated?