Biologists once thought humans had 2 million genes. Now it turns out we have fewer than nematode worms.
Genes are the fundamental units of inheritance in living organisms. Together, they hold all the information necessary to reproduce a given organism and to pass on genetic traits to its offspring.
Biologists have long debated what constitutes a gene in molecular terms but one useful definition is a region of DNA that carries that code necessary to make a molecular chain called a polypeptide. These chains link together to form proteins and so are the bricks and mortar out of which all organism are constructed.
Given this crucial role, it is no surprise that an ongoing goal in biology is to work out the total number of protein-coding genes necessary to construct a given organism. Biologists think the yeast genome contains about 5300 coding genes and a nematode worm genome contains about 20,470.
But the number for humans has been the subject of constant revision since biologists first began the task of estimating them in the 1960s. Then, they believed humans could have as many as 2 million protein-coding genes. But by the time the human genome project began in the late 1990s, the highest estimates put the number at 100,000 and the number has continued to shrink.
In 2001, the initial sequence of the human genome cut the figure dramatically. The International Human Genome Sequencing Consortium put it at 30,000 while a rival group led by Craig Venter estimated the number at 26,000.
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