February 12, 2001

Biologists have been estimating the size of genomes for decades. In 1971, for example, researchers reported that a species of Italian bat, Miniopterus, has a genome half the size of the human genome. Similarly, the genome of Muntiacus, a species of Asian barking deer, was estimated at about 70 percent of that of humans. As reported this week, the human genome contains about 3 billion chemical units of DNA, or base pairs.

In the animal kingdom, the relationship between genome size and evolutionary status is not clear. One of the largest genomes belongs to a very small creature, Amoeba dubia. This protozoan genome has 670 billion units of DNA, or base pairs. The genome of a cousin, Amoeba proteus, has a mere 290 billion base pairs, making it 100 times larger than the human genome.

A Sample of Species and Genome Size (in base pairs)

Amoeba dubia 670,000,000,000
Amoeba proteus 290,000,000,000
Bufo bufo 6,900,000,000
Homo sapiens 2,900,000,000
Muntiacus muntjak vaginalis 2,521,500,000
Boa constrictor 2,100,000,000
Rhinolophus ferrumequinum 1,929,400,000
Plasmodium falciparum 25,000,000
Human immunodeficiency virus type 1 19,750
Source: Database of Genome Sizes (Center for Biological Sequence Analysis)

Among the organisms whose genomes are sequenced, genome size does not correlate with the number of genes.

Species	Size of genome	Number of genes
Human	2.9 billion base pairs	30,000
Fruit fly (Drosophila melanogaster)	120 million base pairs	13,601
Baker's yeast (Saccharomyces cerevisiae)	12 million base pairs	6, 275
Worm (Caenorhabditis elegans)	97 million base pairs	19,000
E. coli	4.1 million base pairs	4,800
Arabidopsis (Arabidopsis thaliana)	125 million base pairs	25,000

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