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The Human Genome Project

DNA Structure, Mapping and Sequencing

DNA Structure, Mapping and Sequencing
Benefits and Ethical Issues


The human genome consists of all the DNA within the cells. The DNA resides within the 46 chromosomes of the human body, which are found in a cell's nucleus. Chromosomes are composed of proteins and nucleic acids. Nucleic acid can be either double stranded (DNA) or single-stranded (RNA). RNA is the molecule that reads and transfers the genetic code to the robosome in the cytoplasm where proteins are formed. DNA, or deoxyribonucleic acid, contains the body's genetic information. DNA has all of the instructions needed for protein and cell formation.


 Nucleotides, the building blocks of nucleic acids, are made up of phosphate, sugar and one of four chemicals called nitrogen bases. The nitrogen bases are Adenine, Thymine, Guamine and Cytosine. One nucleotide is complementary to another and these two fit together by means of a hydrogen bond. Adenine pairs with Thymine, and Guanine pairs with Cytosine. These base pairs assemble in a sequence that makes the double-stranded helix of DNA.

It is estimated that there are approximately 3 billion base pairs of DNA and 100, 000 genes situated on the chromosomes in the human genome. Each gene on a chromosome has a specific sequence of nucleotide bases. It's this order that is used to distinguish one gene from another.



The DNA data used for the Human Genome Project was gathered from the blood or tissue samples of numerous people. The DNA was then analyzed using various mapping and sequencing technologies. The two main categories of gene mapping techniques are:
  • Linkage or Genetic Mapping
  • Physical Mapping

Linkage Mapping
Physical Mapping
  • Uses markers
  • Maps are created mainly by following the inheritance pattern through a family's history.
  • Identifies only the proximate sequence of genes along a chromosome


  • Uses markers
  • Maps are created using mainly robotics, lasers and computers to measure the distance between markers
  • More accurate and can identify specific gene location relative to each other on the chromosome

* Markers are apparent physical or molecular distinctions on the chromosome that differ in people and are passed down through generations

The Human Genome Project predominately used a physical mapping techique in which the DNA is replicated and modified. Each nucleotide base is altered into a fluorescent form of itself. The gene sequence is determined and reconstructed using a computer.
When the project was finished, a tremendous volume of data had been accumulated, including maps of the chromosomes and genes and information regarding the billions of base pair seqences and the hundreds of thousands of markers.