Sequences that cause particular problems for gBlocks Gene Fragment synthesis are those having extremely low or high GC content (less than 25% and greater than 75%), homopolymeric runs of 10 or more As and Ts or 6 or more Gs and Cs. Other structural motifs such as repeats or hairpins may also influence our ability to construct gBlocks Gene Fragments. The decision to accept or reject an order for a particular gBlocks fragment sequence is complex and multifactorial. All of our gBlocks fragments are reviewed by our Gene Specialists prior to manufacturing to ensure the sequences can be made successfully. Questions about gBlocks Gene Fragments? Contact our Gene Specialists directly at firstname.lastname@example.org.