Overhearing

Bill said, "Before the use of vectors in artificial selection reliance for changing alleles was done through mutagenesis" Sue said, "Yes, I agree with you Bill, getting desired traits was done that way, however now the most common way is through the use of vectors and plasmids." Fred then chimed in asking, "What was used before either of those techniques were discovered?" 


Do you know what Bill and Sue are talking about? 
What is the answer to Fred's question?