How big is the human genome?

The size of genomes differs from one organism to the next. It seems likely that a human would have much more DNA than a fly, because humans are so much larger and more complex. However, the complexity of each genome is not necessarily related to its size.

The Human Genome Project is involved in determining the exact order of the DNA bases of the entire human genome. The human genome contains more than 3.4 billion base pairs and between 20 000 and 25 000 genes.

The U.S. Department of Energy Human Genome Project Information Web site illustrates the size of the human genome by estimating that 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 sequence". [Source: Human Genome Projects Information].

Another example of the immensity of the human genome is given by the Centre for Integrated Genomics:

"If our strands of DNA were stretched out in a line, the 46 chromosomes making up the human genome would extend more than six feet [close to two metres]. If the ... length of the 100 trillion cells could be stretched out, it would be ... over 113 billion miles [182 billion kilometres]. That is enough material to reach to the sun and back 610 times." [Source: Centre for Integrated Genomics]

		The largest known genome belongs to a microscopic amoeba, Amoeba Dubia, which is closely followed in size by the lungfish and the Easter lily. Which goes to show that size isn't everything! More about genome size ...

	• What is a genome and why is it so important?   • The human genome   • How big is the human genome?   • Genomics research

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