And we can do this by basically modifying the preexisting genes, by changing the nucleotide sequence in those genes that encode for certain proteins. Now, there are three types of modifications that we can commonly make to our gene. We can modify that gene by deleting a segment of DNA in that gene. We can modify a gene by inserting a segment into that gene, or we can modify it by substitution. Now, in this lecture, we're going to focus on deletions and insertions. In the next lecture, we're going to discuss substitutions.