Cloning systems, DNA molecular weight standards and DNA polymerases for research labs. Tell us the method and the fragment sizes you work with and we suggest the reagents that fit.
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| Product | What it is | Use it for |
|---|---|---|
| Cloning systems | Vectors and enzymes for TA, blunt-end and restriction-based cloning | Inserting PCR products or fragments into plasmids |
| DNA molecular weight standards | Ladders and markers of known fragment sizes | Sizing and roughly quantifying DNA on gels |
| DNA polymerases | Standard Taq, hot-start and proofreading high-fidelity enzymes | Routine PCR, colony screening, cloning-grade amplification |
Polymerases differ in accuracy, speed, the length they can copy and the ends they leave, and each property decides what comes next in the workflow.
| Polymerase | Accuracy | Product ends | Best for |
|---|---|---|---|
| Standard Taq | Baseline; no proofreading | Single 3′ A overhang | Screening, genotyping, TA cloning |
| Hot-start Taq | As Taq, with fewer non-specific products | 3′ A overhang | Low-copy targets, multiplex and qPCR |
| High-fidelity (proofreading) | Many times fewer errors than Taq | Blunt | Cloning, sequencing, mutagenesis |
Proofreading enzymes have a 3′→5′ exonuclease that removes misincorporated bases. Their blunt products need A-tailing for TA vectors, or a blunt or assembly cloning method instead.
A ladder is only useful when its bands bracket your fragment on the gel you run. Match the ladder to the range, and the agarose percentage to both.
| Your fragments | Ladder | Agarose |
|---|---|---|
| Under 1 kb (PCR products) | 50 bp or 100 bp ladder | 1.5–2% |
| 0.5–10 kb | 1 kb ladder | 0.8–1% |
| 100 bp to 10 kb in one gel | Broad-range ladder | 1% |
| Above 10 kb (genomic DNA) | High molecular weight marker | 0.5–0.7% |
The DNA ladder guide covers loading amounts, staining and using reference bands to estimate concentration.
The molecular cloning workflow guide explains each step and its common failure points, and plasmid kits cover the miniprep.
The terms are used almost interchangeably. A ladder usually means evenly spaced bands, such as every 100 bp. Marker sometimes refers to a restriction digest of a known DNA, like lambda DNA cut with HindIII, which gives unevenly spaced bands.
Standard or hot-start Taq, which adds a single A to the 3′ ends of its products. If you amplified the insert with a proofreading enzyme for accuracy, add A overhangs with Taq in a short extra incubation, or use blunt-end cloning instead.
Ladders are designed and sized for agarose gels. Small-fragment ladders often run well on polyacrylamide, but apparent sizes can shift, so check the datasheet before relying on them.
At -20 °C in their glycerol storage buffer, in a freezer that does not cycle through defrost. Take them out only as long as needed and keep them in a cold block or on ice.
Yes. Colony PCR and restriction digests confirm size and orientation, but only sequencing confirms there are no point mutations in the insert or at the junctions.
Molecular biology
A DNA ladder is only useful if its bands bracket your fragment on the gel you are running. This guide matches ladder ranges to agarose percentages and covers loading, staining and quantification.
4 minute read
Molecular biology
Cloning is a chain of small steps, and most failures trace back to one of them. Here is the whole chain, the reagent each step needs, and how to check you have the right clone before you build on it.
4 minute read
Molecular biology
Read the gel first. No band, a smear, extra bands and a fuzzy band under 100 bp each point to a different change, and the positive control tells you whether to trust the mix.
3 minute read
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