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Happy 10th Anniversary, Human Genome Project
#1
Twenty three years ago, in 1990, scientists began working together on one of the largest biological research projects ever proposed. The project proposed to sequence the 3 billion nucleotides in the human genome. It was met with great hope, from discovering the causes of many human diseases, to the eventual discovery of new treatments for these diseases. The project took 13 years to complete, at a cost of approximately three billion dollars.

When the project began, scientists estimated they would find about 100,000 distinct genes in the human genome. As the project progressed, they were stunned to find humans had only about 25,000 genes. How could an organism as complex as a human being have a number of genes similar to that of a worm? The answer was alternative splicing. Splicing is a process that occurs during transcription, or the production of mRNA, in eukaryotic cells. Introns, which are noncoding regions of nucleotides, are removed, while the exons, the coding regions, are fused, or spliced, together. This forms a mature mRNA that can direct protein production. Sometimes, though, different combinations of exons may be spliced together. These different combinations of exons allow one gene to code for the production of multiple proteins.

Another surprise to scientists was how difficult it was to determine the functions of the genes that were sequenced during the human genome project. Sequencing the genome merely told scientists which of the four DNA bases was in each position in the human genome. After the genome was sequenced, scientists had to begin the process of determining what function each gene has. Some genes had already been studied, and were easily identified after the genome was sequenced. Others were, and still are, unknown. Alternative splicing patterns, which can create multiple proteins from a single gene, further complicate the determination of gene function.

In addition to sequencing the coding regions of DNA, which tell the cell how to make proteins, scientists are now interested in determining the function of noncoding, or junk, regions of DNA. These repetitive nucleotide sequences are found in every person’s genome, and make up approximately 98% of the bases. For many years, scientists believed that these noncoding sequences had no function. They were believed to be made of remnants of retroviruses that had previously integrated into the genome and had since become inactive. Transposons, pieces of DNA that can move from one location to another, are also believed to be a component of the junk DNA. In recent years, scientists have noticed that noncoding DNA may actually play a role in the cell. Some of this junk DNA may actually function as transcription factors. These are sequences of DNA that help recruit the enzymes required for transcription of DNA into mRNA. Another idea is that the junk DNA provides variation in the population, which is important for helping the human population continue to evolve. These sequences might even help explain differences between humans and other closely related animals. This may be directly linked to the transcription factors found in noncoding DNA. The timing and amount of gene expression may lead to many of the differences between humans and other mammals.

As with many scientific endeavors, the human genome project generated far more questions than answers. However, the information gained must not be undersold. In addition to learning more about how genes function, we have developed exponentially superior technology over the past ten years. While the human genome project took 13 years and cost billions of dollars, a normal human genome can be sequenced in a few days and a cost of only a few thousand dollars. The technology has become faster, more widely available, and cheaper. Individual genome sequencing is already being used to help people determine their risk for various genetically –linked disorders. Rapid and affordable genome sequencing is also helpful for researchers who want to find differences between patients afflicted with a disorder, and volunteers without the disorder. Because of the research resulting from the sequencing of the human genome, scientists have links between genes and many human disorders, including cancer, some neurodegenerative disease, and more. By studying the defects in genes that cause these disorders, researchers might be more able to develop rational treatments. Indeed, many advancements have been made in the past 10 years, and many more are sure to come in the next 10.


References:

http://news.yahoo.com/human-genome-proje...31005.html

http://www.nytimes.com/2013/04/16/scienc....html?_r=0

http://www.sciencedaily.com/releases/200...180928.htm
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#2
The human genome (DNA) is made up of 23 billion base pairs.

It possess about 50000 – 100000 genes and is aligned as a set of 23 chromosomes.

Of the 3 billion base pairs only about 20 -30 percent are genes and related sequences whereas remaining 70- 80 percent are extragenic DNA

The gene and gene related sequence is comprised of coding (less than 10 percent) and non-coding sequence (greater than 90 percent)

The coding sequences are called as Exons.

Introns, promoters, leaders or trailers, pseudogenes and gene fragments form the non-coding sequence.

The extragenic DNA is comprised of about 20-30 percent of moderative or highly repetitive sequences and about 70 – 80 percent of unique or low copy numbers.

The repetitive sequences occur as dispersed repeats (40 percent) and clustered repeats (60 percent).

SINEs and LINEs are dispersed repetitive sequence whereas satellite DNA, mini satellite DNA and microsatellite DNA are clustered repetitive sequence.

Glossary

Exons: Coding regions of DNA

Introns: Non coding regions separating exons

Leader and Trailer sequence: These sequences being present at the 5 prime and 3 prime ends of the DNA are subjected only to transcription and restricted from being translated

Promoter sequence: Being positioned at the transcription initiation spot this sequence enables the synthesis of mRNA

Pseudogenes: Mutated form of the original gene and thus no more active participation in protein production. Pseudogenes are results of nonsense mutation

Gene Fragments: Non functional groups of fragments whose either 5 prime or 3 prime region is absent

SINE: Short Interspersed Nuclear Elements. Alu element is one of the examples for SINE

LINE: Long Interspersed Nuclear Elements. L1 LINE is one of the examples for LINE

Satellite DNA: Clusters of repetitive sequence in the human genome which is of about 100 to 5000kbp in length

Minisatellite DNA: Repetitive sequence clusters which is of about 100 base pairs to 20 kbp in length

Microsatellite DNA: Short length repetitive sequence which is less than or equal to 4 base pairs
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Happy 10th Anniversary, Human Genome Project00