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Human Genome

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All these ACGTs. What are they?

Over three billion of them from a human form the human genome - the human genetic material - all the information needed to encode a human being. It would take about 9.5 years to read out loud - without stopping - the more than three billion pairs of bases in one person's genome.

The Human Genome

What makes each one of us unique? You could argue that the environment plays a role, and it does to some extent. But most would agree that your parents have something to do with your uniqueness. In fact, it is our genes that make each one of us unique – or at least genetically unique. We all have the genes that make us human: the genes for skin and bones, eyes and ears, fingers and toes, and so on. However, we all have different skin colors, different bone sizes, different eye colors and different ear shapes. In fact, even though we have the same genes, the products of these genes work a little differently in most of us. And that is what makes us unique.

The human genome is the genome - all the DNA - of Homo sapiens . Humans have about 3 billion bases of information, divided into roughly 20,000 to 22,000 genes, which are spread among non-coding sequences and distributed among 24 distinct chromosomes (22 autosomes plus the X and Y sex chromosomes ) ( below ). The genome is all of the hereditary information encoded in the DNA, including the genes and non-coding sequences.

Human Genome, Chromosomes, and Genes. Each chromosome of the human genome contains many genes as well as noncoding intergenic (between genes) regions. Each pair of chromosomes is shown here in a different color.

Thanks to the Human Genome Project , scientists now know the DNA sequence of the entire human genome. The Human Genome Project is an international project that includes scientists from around the world. It began in 1990, and by 2003, scientists had sequenced all 3 billion base pairs of human DNA. Now they are trying to identify all the genes in the sequence. The Human Genome Project has produced a reference sequence of the human genome. The human genome consists of protein-coding exons , associated introns and regulatory sequences, genes that encode other RNA molecules, and “junk” DNA - regions in which no function as yet been identified.

You can watch a video about the Human Genome Project and how it cracked the "code of life" at this link: http://www.pbs.org/wgbh/nova/genome/program.html .

Our Molecular Selves video discusses the human genome, and is available at http://www.genome.gov/25520211 or http://www.youtube.com/watch?v=_EK3g6px7Ik . Genome, Unlocking Life's Code is the Smithsonian's National Museum of Natural History exhibit of the human genome. See http://unlockinglifescode.org to visit the exhibit.

ENCODE: The Encyclopedia of DNA Elements

In September 2012, ENCODE, The Enc yclopedia o f D NA E lements, was announced. ENCODE was a colossal project, involving over 440 scientists in 32 labs the world-over, whose goal was to understand the human genome. It had been thought that about 80% of the human genome was "junk" DNA. ENCODE has established that this is not true. Now it is thought that about 80% of the genome is active. In fact, much of the human genome is regulatory sequences, on/off switches that tell our genes what to do and when to do it. Dr. Eric Green, director of the National Human Genome Research Institute of the National Institutes of Health which organized this project, states, "It's this incredible choreography going on, of a modest number of genes and an immense number of ... switches that are choreographing how those genes are used."

It is now thought that at least three-quarters of the genome is involved in making RNA, and most of this RNA appears to help regulate gene activity. Scientists have also identified about 4 million sites where proteins bind to DNA and act in a regulatory capacity. These new findings demonstrate that the human genome has remarkable and precise, and complex, controls over the expression of genetic information within a cell.

See ENCODE data describes function of human genome at http://www.genome.gov/27549810 for additional information.

Summary

  • The human genome consists of about 3 billion base pairs of DNA.
  • In 2003, the Human Genome Project finished sequencing all 3 billion base pairs.

Practice

Use this resource to answer the questions that follow.

  1. What were 3 goals of the Human Genome Project?
  2. How many genes are on chromosome #1?
  3. How big is the human genome?
  4. How much genetic variation is there among people?
  5. How much of the genome is not part of any gene?

Review

1. Describe the human genome.

2. What has the Human Genome Project achieved?

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