What is the Difference Between Clone by Clone Sequencing and Shotgun Sequencing?

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Clone-by-clone sequencing and shotgun sequencing are two different strategies for whole genome sequencing. The main differences between these two methods are:

  1. Mapping and Cloning: Clone-by-clone sequencing involves mapping of chromosomes and cloning prior to sequencing, while shotgun sequencing omits both of these steps.
  2. Sequencing Process: Clone-by-clone sequencing minimizes the number of sequencing reactions required and makes sequence assembly straightforward and reliable. Shotgun sequencing, on the other hand, sequences first and does not require a physical map. It breaks the genome into fragments that are small enough to be sequenced and then reassembles them by looking for overlaps in the sequence of each fragment.
  3. Number of Sequencing Reactions: Shotgun sequencing requires many more sequencing reactions than the clone-by-clone method because it involves sequencing redundant fragments.
  4. Speed and Cost: Shotgun sequencing is generally faster and cheaper than clone-by-clone sequencing, as it avoids the laborious process of making a physical map.

Both methods involve breaking the genome into smaller fragments and reassembling them by identifying overlapped regions. However, clone-by-clone sequencing is considered more reliable, while shotgun sequencing is faster and cheaper.

Comparative Table: Clone by Clone Sequencing vs Shotgun Sequencing

Clone-by-clone sequencing and shotgun sequencing are two different methods used for genome sequencing. Here is a table comparing the main differences between the two methods:

Feature Clone-by-clone sequencing Shotgun sequencing
Method Involves cloning and genome mapping before sequencing. Randomly breaks up DNA sequences into many small fragments and reassembles the sequence.
Mapping Requires the creation of a physical map before sequencing. Avoids the laborious process of making a physical map.
Sequencing reactions Minimizes the number of sequencing reactions. Requires many more sequencing reactions than the clone-by-clone method due to sequencing redundant fragments.
Assembly Assembly is straightforward and reliable, as it is based on the physical map. Assembly relies on looking for overlaps in the sequence of each fragment.
Fragments Fragments are larger in size, ranging from 20 kb to 300 kb. Fragments are smaller and randomly sequenced.
Time-consuming More time-consuming, as it involves genome mapping and cloning steps. Less time-consuming, but still requires the assembly process to be carried out using sophisticated computer software.
Reliability More reliable, as it is based on the physical map. Less reliable, but still widely used in modern molecular biology.
Preferred method Preferred during the Human Genome Project. Become the current standard methodology, with many large human and other genomes having been sequenced successfully.

In summary, clone-by-clone sequencing is a more reliable method that involves mapping the genome before sequencing, while shotgun sequencing is a faster and cheaper method that directly sequences random DNA fragments and reassembles them based on overlaps. The choice of method depends on the specific goals and constraints of the sequencing project.