How did hierarchical shotgun sequencing work in the Human Genome Project?

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The impact of the Human Genome Project on cancer research — Human Genome Project The Human Genome Project, which operated from 1990 to 2003, provided researchers with basic information about the genetic content of the human organism, opening new avenues of discovery in fields such as cancer research.

Hierarchical shotgun sequencing was a foundational method used during the Human Genome Project to generate high-quality reference sequences. The process functioned through the following steps:

Physical Mapping: Large genomic DNA was first broken down and cloned into ordered arrays known as physical maps. These maps served as a framework to organize the genome into thousands of manageable, smaller DNA fragments.1
Fragmentation and Amplification: These segments were further fragmented into even smaller pieces and inserted into bacterial cells as plasmids. This allowed for the amplification of the DNA, producing the many copies necessary for accurate sequence analysis.1
Alignment and Assembly: The resulting short sequences were aligned by identifying overlapping identical regions. This allowed scientists to link the fragments together to reconstruct the full-length genomic sequence.1

This hierarchical approach was favored for its ability to produce high-quality, reliable reference sequences, as the smaller fragments were easier to manipulate in the laboratory and allowed for detailed error-correction by collaborating research teams.1