What is a gene?: MedlinePlus Genetics

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<span>What is a gene?</span> </div> </div> </div> <span class="page-url print-only">URL of this page: https://medlineplus.gov/genetics/understanding/basics/gene/</span> <div > <article> <div class="page-info"> <div class="page-title"> <a name="start" id="start"></a> <h1>What is a gene?</h1> </div> <div class="page-actions"></div> <noscript><span class="js-disabled-message">To use the sharing features on this page, please enable JavaScript.</span></noscript> </div> <div class="main"> <section><div class="mp-content"><p>A gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as <a data-pid="20147" href="https://medlineplus.gov/genetics/understanding/howgeneswork/makingprotein/">instructions</a> to make molecules called proteins, which are needed for the body to function. However, many genes <a data-pid="20115" href="https://medlineplus.gov/genetics/understanding/basics/noncodingdna/">do not code for proteins</a>, instead they help control other genes. </p><p>The information in DNA is encoded in genetic building blocks called base pairs. In humans, genes vary in size from a few hundred DNA base pairs to more than 2 million base pairs. Between 1990 and 2003, an international research effort called the Human Genome Project worked to sequence all of the DNA in a human (known as the human genome). The project estimated that humans have between 20,000 and 25,000 genes that provide instructions for making proteins. Later studies sought to build on the work of the Human Genome Project and have provided additional details on the genome sequence. We now know that the human genome contains about 19,900 genes used to produce proteins.</p> <p>Typically, people have two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. Forms of the same gene with small differences in their sequence of DNA bases are called alleles. These small differences contribute to each person’s unique physical features.</p> <p>Scientists keep track of genes by giving them unique names. Because gene names can be long, genes are also assigned symbols, which are short combinations of letters (and sometimes numbers) that represent an abbreviated version of the gene name. For example, one of the genes on <a data-pid="20043" href="https://medlineplus.gov/genetics/chromosome/7/">chromosome 7</a> is called the cystic fibrosis transmembrane conductance regulator because variants in this gene can cause <a data-pid="14435" href="https://medlineplus.gov/genetics/condition/cystic-fibrosis/">cystic fibrosis</a>. The symbol for this gene is<em> </em><a data-pid="17111" href="https://medlineplus.gov/genetics/gene/cftr/"><em>CFTR</em></a>.</p> <div class="mediaobject"><div class="caption"><p>Genes are made up of DNA. Each chromosome contains many genes.</p></div> <div class="imagedata"><img alt="A gene is labeled along the length of a chromosome." height="240" src="https://medlineplus.gov/images/PX00006G_PRESENTATION.jpeg" width="500"/></div> <div class="image-credit">Credit: U.S. National Library of Medicine</div></div></div> </section> </div> <div class="side"> <aside> <section><div class="side-section"><div class="mp-content"><div class="section-header long-header"> <h2>For more information about genes:</h2> </div> <div class="section-body"> <p>MedlinePlus Genetics provides <a data-pid="17013" href="https://medlineplus.gov/genetics/gene/">consumer-friendly gene summaries</a> that include an explanation of each gene's normal function and how variants in the gene cause particular genetic conditions.<span class="desc-text"><img alt="From the National Institutes of Health" class="imgdesc" height="16" src="https://medlineplus.gov/images/nih.png" title="From the National Institutes of Health" width="25"/></span></p> <p>More information about <a data-pid="20143" href="https://medlineplus.gov/genetics/understanding/mutationsanddisorders/naming/">how genetic conditions and genes are named</a> is also available from MedlinePlus Genetics.<span class="desc-text"><img alt="From the National Institutes of Health" class="imgdesc" height="16" src="https://medlineplus.gov/images/nih.png" title="From the National Institutes of Health" width="25"/></span></p> <p>The National Human Genome Research Institute provides information on the <a href="https://www.genome.gov/human-genome-project">Human Genome Project</a> and <a href="https://www.genome.gov/about-genomics/telomere-to-telomere">Telomere 2 Telomere</a>, two studies that were pivotal in providing a complete sequence of the human genome. The National Human Genome Research Institute also includes additional information about <a href="https://www.genome.gov/About-Genomics/Introduction-to-Genomics#one">gene and the genome</a>.<span class="desc-text"><img alt="From the National Institutes of Health" class="imgdesc" height="16" src="https://medlineplus.gov/images/nih.png" title="From the National Institutes of Health" width="25"/></span></p> <p>The Centre for Genetics Education offers <a href="https://www.genetics.edu.au/SitePages/DNA-RNA-genes-and-chromosomes.aspx" rel="noopener noreferrer" target="_blank">a fact sheet that introduces genes and chromosomes</a>.</p> <p>The Virtual Genetics Education Centre, created by the University of Leicester, offers additional information on <a href="https://le.ac.uk/vgec/topics/dna/dna-higher-education" target="_blank">DNA, genes, and chromosomes</a>.</p> <p>An article published in the journal <em>Science</em> in 2022, “<a href="https://pubmed.ncbi.nlm.nih.gov/35357919/">The complete sequence of a human genome</a>,” provides updated information on the human genome.</p> </div></div> </div></section> </aside> </div> <div class="bottom"> <section><div class="mp-exp mp-content"><h2>Topics in the Cells and DNA chapter</h2><ul><li><a data-pid="20105" href="https://medlineplus.gov/genetics/understanding/basics/cell/">What is a cell?</a></li><li><a data-pid="20107" href="https://medlineplus.gov/genetics/understanding/basics/dna/">What is DNA?</a></li><li>What is a gene?</li><li><a data-pid="20111" href="https://medlineplus.gov/genetics/understanding/basics/chromosome/">What is a chromosome?</a></li><li><a data-pid="20113" href="https://medlineplus.gov/genetics/understanding/basics/howmanychromosomes/">How many chromosomes do people have?</a></li><li><a data-pid="20115" href="https://medlineplus.gov/genetics/understanding/basics/noncodingdna/">What is noncoding DNA?</a></li></ul><p><a data-pid="20081" href="https://medlineplus.gov/genetics/understanding/">Other chapters in Help Me Understand Genetics</a></p></div> </section> <section>  <p>The information on this site should not be used as a substitute for professional medical care or advice. 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What is a gene?: MedlinePlus Genetics