Describe the stages that are used to genetically modify yeast cells so that they are able to produce the enzyme chymosin (used in cheese-making).

Chymosin is a protease enzyme that clots milk.

Explain what is meant by the term enzyme.

Traditional dairy farming often uses selective breeding rather than genetic modification to improve milk production. Describe how selective breeding could be used to produce a herd of cows with a high milk yield.