Human genome project

Introduction

The human genome project was one of the challenging projects launched in the year 1990. The main aim of this was to find out the complete DNA sequence of the human genome by using the modern genetic engineering technique-Bio-informatics. It was used to isolate and clone the DNA segment. Till date, it remains as one of the largest biological projects in the world.

       

Table of Contents

1. Introduction

2. Main Goals of HGP

3. Methodology used in HGP

4. Important Features of the Human Genome

5. Phases of HGP

6. DNA fingerprinting

7. Procedure for DNA fingerprinting

 

                                                                                                                                                                                      

 

 

 

 

 

 

 

 

 

 

 

 

Main Goals of HGP

  1. To identify all 20,000-25,000 genes present in human DNA.

  2. To determine the exact sequences of the 3 billion chemical base pairs that make up human DNA.

  3. To store the information found by the project in databases.

  4. To develop and improve tools for data analysis related to the project.

  5. To transfer project-related technologies to other sectors like industries.

  6. To address the ethical, legal, and social issues (ELSI) that may arise from the project.

HGP was a 13-year long project coordinated by the department of energy and the National Institute of Health of the United States of America. The other partners who contributed were, U.K, Japan, France, Germany, China, and others. The project was ended in the year 2003. 

 

Methodology used in HGP

  1. Since DNA sequencing was the core idea behind the project, various physical and chemical techniques experimented on genes that help in sequencing the DNA. Those techniques were aimed at determining the order of the nucleotide bases like adenine, guanine, cytosine, and thymine in a molecule of DNA.

  2. Among all, the most common methods used were, firstly,  the Maxam Gilbert technique which uses chemicals to breakdown the DNA into small pieces at specific bases and the second technique is popularly known as the Sanger technique or di-deoxy or chain-terminating method. In the second technique, new DNA chains were formed by using DNA polymerase( in the presence of dideoxynucleotides chain terminators).

  3. By using polyacrylamide gel electrophoresis, the DNA fragments were separated according to the length required. Such separation has enabled the sequence to be read directly from the gel.

  4. In addition to these 2 techniques, Employment of Restriction Fragment-Length Polymorphisms (RFLP), Yeast Artificial Chromosomes technique, bacterial artificial chromosomes (BAC) were also used as cloners that are helpful in the construction of genomic libraries for genome-scale sequencing projects.

 

Important Features of the Human Genome

  1. The human genome has about a total of 3164.7 million nucleotide bases.

  2. An average gene consists of 3000 bases with varied sizes. The largest human gene is dystrophin that contains 2.4 million bases.

  3. The total number of genes in the genome is approximately 30,000 and 99.9 % of their nucleotide bases are exactly the same in every person.

  4. Almost 50% of the discovered genes have some functions but are not completely understood.

  5. Less than 2% of the genes of the genome assists in coding for protein synthesis.

  6. Chromosome 1 has the most genes about 2968 and among the sex chromosomes, Y has the fewest chromosomes-231.

  7. Repeated sequences (AT-AT-AT or GC-GC-GC etc,) make up a very large portion of the human genome.

  8. Scientists found that over 1.4 million locations have a single base DNA differences (SNPs-single nucleotide polymorphism, pronounced as ‘snips’) that occur on humans.

 

Phases of HGP

The project couldn't sequence the genome found in the centromeres, telomeres and heterochromatin regions, however, the project has successfully mapped the genomes within euchromatic regions. Euchromatic make up 92.1% of the total human genome.  , and were not sequenced under the project. The project has submitted an initial rough draft in June 2000 and by February 2001 a working draft had been completed followed by the final sequencing mapping of the human genome on April 14, 2003.

 

DNA fingerprinting

It is otherwise known as DNA typing, DNA profiling, genetic fingerprinting, genotyping, or identity testing, in genetics. DNA fingerprinting is a method of isolating and finding out the variable elements within the base-pair sequence of DNA. It was first developed in 1984 by British geneticist Alec Jeffreys. He found that certain sequences of highly variable DNA (also called mini satellites), have no role as genes and they are repeated within the normal genes. Jeffreys was successful to find out that, each individual has a unique pattern of mini-satellites except in the case of identical twins born by the same zygote after fertilization.

 

Procedure for DNA fingerprinting

  1. The procedure includes, obtaining a sample of cells like the small scrape of skin, hair, or blood cells and then the DNA is extracted from these cells and purified.

  2. Later on, by using chemical techniques, this DNA is cut at specific points along the strand with proteins known as restriction enzymes.

  3. After cutting into fragments, the enzyme-treated fragments were sorted by placing them on a gel and then subjecting them to electrophoresis which uses electric current.

  4. At this stage, sorted double-stranded DNA fragments were put into a process called blotting. During the blotting process, they were made into single strands and then transferred to a nylon sheet.

  5. Such fragments were subjected to auto-radiography where they were exposed to DNA probes. The DNA radio probes are synthetic DNA that were made radioactive by exposing them to  X-ray film and this has led to dark mark. These patterns of marks could then be analyzed.





img-1

img-1

img-1

Course List