1. In the human thyroid gland the amino acid tyrosine is converted by a series of reactions into the hormone thyroxine. Insufficient thyroxine production may lead to mental and physical retardation.

In about 1 in 5000 children, one of the enzymes involved in thyroxine production does not function effectively. The ineffective enzyme is a result of a gene mutation
(a) (i)  Give one way in which a gene mutation like this may have arisen.



(ii) Give one factor which might increase the frequency at which gene mutation occurs.



(b)  Explain how a gene mutation may result in the production of an ineffective enzyme





2. Mutations to DNA can affect the proteins produced by cells
(a) Explain why a base deletion mutation, may have a greater effect than a base substitution mutation




(b) Name two agents, which can cause mutations.