If the dna sequence ttcacg is transcribed to aaggc, what type of mutation has occurred?

Insertion

Genetic stability maintenance  requires an extremely accurate mechanism for DNA replication and mechanisms for fixing the several accidental lesions that occur continually in DNA.  Spontaneous changes in DNA are temporary due to immediate correction process called DNA repair. DNA repair’s importance is very evident from the huge investment that cells form in DNA repair enzymes. In 1000 accidental base changes in DNA , fewer than one results in a permanent mutation due to the efficient elimination by the DNA repair. 

Yes he thought they should be left to chance why, because he thought that was the best thing to do