Gene targeting can be used to study the function of a gene. Which of the statements describing gene targeting are true?
I. The use of gene targeting is limited to model organisms, such as rats, where gene targeting methods are well established.
II. Gene targeting can be used to introduce a point mutation into an existing gene to observe what happens when the gene is modified.
III. Gene targeting to delete a gene can be performed on an adult organism so that the before and after effects can be observed.
IV. Gene targeting can be used to turn off a gene to observe what happens when the gene is not expressed.