Synthetic Biology
Support and Educational Content

Easy gene assembly—gBlocks® custom dsDNA gene fragments

  • Highly versatile—gBlocks Gene Fragments can be used to easily and reliably assemble almost any sequence, and are compatible with most published cloning methods, including the Gibson Assembly® Method, and blunt-end or cohesive-end cloning protocols.
  • Easy isothermal gene assembly—Using the Gibson Assembly Method, multiple gBlocks Gene Fragments can be assembled into a larger gene construct, in a single reaction that takes about 1 hour. A simple, 20–80 nt sequence overlap is required when designing the gene fragments for assembly.
  • Affordable—gBlocks Gene Fragments are up to half the price of other synthetic gene constructs, making synthetic biology accessible to any lab.
  • Short delivery time—gBlocks Gene Fragments are typically shipped within 5–8 business days.

Figure 1. gBlocks® Gene Fragments make it easy to produce the correct synthetic genes. gBlocks Gene Fragments (n=43), ranging from 126 to 459 bp and with GC ratios between 40 and 70%, were synthesized and cloned into pIDTSMART-Amp by blunt-end cloning. Ligated plasmids were transformed into XL1Blue cells, and 3–25 clones for each gBlocks Gene Fragment were selected and sequenced using traditional Sanger sequencing. The average fidelity for all sequences analyzed was 90%, and for 40 out of 43 gBlocks Gene Fragments the correct sequence was observed in >80% clones. The high percentage of correct sequences obtained makes it easy to find your desired clone.

High-fidelity, double-stranded DNA sequences

gBlocks Gene Fragments are sequence-verified, double-stranded DNA fragments, 125–3000 bp in length, that enable easy gene construction or modification. They are synthesized using the highest fidelity synthesis methods, developed by IDT for our industry-leading Ultramer™ Oligonucleotides, making them ideal for a broad range of cloning techniques.

Screen fewer clones

Experimental data shows that 90% of cloned gBlocks Gene Fragments will have the correct sequence (Figure 1). In addition, using the Gibson Assembly method, two or more gBlocks fragments can easily be assembled in a single reaction to generate larger constructs [1] (Table 1). gBlocks Gene Fragments are synthesized without a 5’ phosphate; optional 5’ phosphorylation is available for blunt cloning.

Table 1. Isothermal Assembly of Multiple gBlocks® Gen Fragments. EGFP and Kanamycin genes were assembled from 2 and 3 gBlocks Gene Fragments respectively and cloned into a linearized pUC57 vector using the Gibson Assembly method [1]. Cloned sequences were verified by double-stranded Sanger sequencing. The results show that even when assembling 3 fragments, gBlocks Gene Fragments make gene construction a highly reliable process.

Get gBlocks Gene Fragments quickly

The easy online ordering system allows sequences for gBlocks Gene Fragments to be entered individually or as multiple entries using a provided Microsoft Excel template. Orders typically ship within 5–8 business days. gBlocks Gene Fragments are delivered with a short protocol that summarizes cloning methods for experienced users. Complete assembly and cloning protocols are available under Support on the gBlocks Gene Fragments product page.


  1. Gibson DG, Young L, et al. (2009) Enzymatic assembly of DNA molecules up to several hundred kilobases. Nature Methods, 6(5):343–345.

Product focus—custom dsDNA fragments and codon optimization

gBlocks® Gene Fragments

These double-stranded, sequence-verified, DNA genomic blocks, 125–3000 bp in length, are designed by you, and are shipped in 2–5 working days for affordable and easy gene construction or modification. They have been used in a wide range of applications including CRISPR-mediated genome editing, antibody research, codon optimization, mutagenesis, and aptamer expression. They can also be used for generating qPCR standards.

gBlocks Gene Fragments Libraries

gBlocks Gene Fragments are also available as dsDNA fragment pools that contain up to 18 consecutive variable bases (N or K) for recombinant antibody generation or protein engineering.

Learn more about gBlocks Gene Fragments at

Codon Optimization Tool

The IDT Codon Optimization Tool simplifies designing synthetic genes and gBlocks® Gene Fragments for expression in a variety of organisms. It optimizes a DNA or protein sequence from one host organism for expression in another by re assigning codon usage. You can easily adjust a sequence that has difficult secondary structure, a repetitive motif, or high/low GC content for compatibility with gene or gBlocks Gene Fragments manufacturing requirements. Further, manual optimization allows you to make desired changes to individual codons by simply clicking on their locations.

Access IDT's free, online Codon Optimization Tool and get started.

Additional reading

Learn more about gBlocks Gene Fragments and their applications:

  • Easily designed standard curves for qPCR—Use synthetic gBlocks Gene Fragments for creating standard curves, including incorporating multiple targets into a single gene fragment.
  • Site-directed mutagenesis—improvements to established methods—Site-directed mutagenesis techniques have relied primarily on PCR and standard cloning methods. Read about some of the common cloning methods used for mutagenesis and how double-stranded DNA fragments (gBlocks® Gene Fragments) can save you both time and money.
  • Pakistani iGEM team’s biosensor detects vehicle emission levels—Research profile: Learn how the first ever Pakistani iGEM team developed a portable, inexpensive vehicle emissions test to address air pollution. They used gBlocks Gene Fragments for construction of CO- and NOx-detecting genetic circuits. The colorimetric biosensor won this young research team a bronze medal at the 2016 iGEM International Jamboree.
  • Measuring promoter-driven transcriptional noise in E. coli—Research profile: See how gBlocks® Gene Fragments facilitated the College of William & Mary’s iGEM project on promoter stochasticity (“noise”), which won the Grand Prize at the 2015 iGEM Giant Jamboree. The team applied Elowitz’s promoter evaluation method to the 3 most frequently used promoters in the iGEM BioBrick registry and found significant differences in promoter function.
  • Czech Republic iGEM team’s diagnostic for circulating tumor cells—Research profile: Read how students participating on the Czech Republic’s first iGEM team reprogrammed yeast cells to identify circulating tumor cells. Their project, the IOD Band, could become a general diagnostic test for early detection and mapping of tumor cell mobility. IDT gBlocks® Gene Fragments facilitated rapid, construct assembly of IOD Band receptor molecules.

Review other DECODED Online newsletter articles on synthetic biology applications.

You can also browse our DECODED Online newsletter for additional application reviews, lab tips, and citation summaries to facilitate your research.

Author: Hans Packer is a scientific writer at IDT.

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gBlocks® Gene Fragments

Double-stranded DNA up to 3,000 kb—great for easy gene construction, CRISPR genome editing, and more.

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