Donor DNA - the DNA sequence you want to take from one source and insert into another DNA molecule 1. Genomic DNA - Taken directly from an organisms genome. EX) if you take the human gene for insulin directly from a human chromosome, you're using genomic DNA -Genomic DNA contains introns (non-coding sections within genes) that bacteria can't remove when making proteins 2. cDNA Complementary DNA - Made from using mRNA as a template by using an enzyme called reverse transcriptase - DNA -> mRNA -> cDNA - Useful for expressing eukaryotic genes in bacteria because the introns don't exist in mRNA (it just has coding information) 3. Chemically synthesized DNA - DNA sequence is artificially made in a lab (don't need to take from a cell) - Machines synthesize DNA and scientist insert it into a plasmid - Useful when the exact sequence wanted is known, when you want to modify the sequence, and when you want to make a completely new DNA sequence - No DNA template is needed (unlike cells - a strand is needed as a template)