To solve this problem, we need to identify the sequence that controls the copy number of the linked DNA in a vector. Let's analyze each option:$\newline \bullet$Option 1: Ori site$\newline$ - The Ori site, or origin of replication, is a sequence in a genome where replication is initiated.$\newline$ - It is responsible for controlling the copy number of the DNA linked to it in the vector.$\newline$ - Therefore, the Ori site is the correct sequence that controls the copy number.$\newline \bullet$Option 2: Palindromic sequence$\newline$ - A palindromic sequence is a sequence of nucleotides that reads the same forward and backward.$\newline$ - It is often recognized by restriction enzymes but does not control the copy number of DNA.$\newline \bullet$Option 3: Recognition site$\newline$ - A recognition site is a specific sequence of nucleotides recognized by restriction enzymes.$\newline$ - It is used for cutting DNA at specific locations but does not control the copy number.$\newline \bullet$Option 4: Selectable marker$\newline$ - A selectable marker is a gene introduced into a cell to provide a trait suitable for artificial selection.$\newline$ - It is used to identify cells that have taken up foreign DNA but does not control the copy number.$\newline$Based on the analysis, the correct option is:$\newline$Option 1: Ori site$\newline$This corresponds to the correct option, which is Option 1.