Mapping The Human Genome

In 1990, geneticists around the world tackled one of the most ambitious projects in scientific history—the Human Genome Project. The Human Genome Project is a research effort undertaken to sequence all of our DNA and locate within it all of the functionally important sequences, such as genes. That is, the project seeks to determine the sequence of all 3.3 billion nucleotides of the human genome and to map the location of every gene on each chromosome. Information from the project will provide insight into our evolutionary past, genome organization, gene expression, and cell growth.

The Human Genome Project linked more than 20 scientific laboratories in six countries. By 2001, the draft sequence of the human genome appeared in two landmark papers in the science journals Science and Nature. The high-quality sequence was completed in 2003—two years ahead of schedule. Figure 13-7 shows an example of how the sequence of nucleotides in a piece of DNA is displayed on a computer screen.

Important Insights

Scientists with the Human Genome Project were surprised by some of the discoveries they made, including the following:

1. Only about 2 percent of the human genome codes for proteins.

2. Chromosomes have unequal distribution of exons—sequences of nucleotides that are transcribed and translated.

3. The human genome is smaller than previously estimated. The human genome has only about 20,000 to 25,000 protein-coding genes—far fewer than the 100,000 originally estimated. Scientists now know that RNAs are not used only for translating DNA into proteins. Many RNAs are involved in regulating gene expression.

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