About how many protein-coding genes does the finished human genome sequence contain?
- About 2,000
- About 100,000
- About 500,000
- About 20,000
Why D? And why not the others?
Correct answer: D. About 20,000
The finished human genome sequence, published in 2004, settled the protein-coding gene count at roughly 20,000, far lower than genome scientists had guessed before sequencing was complete. The real surprise is comparative: the tiny roundworm C. elegans, a transparent worm with only about a thousand cells total, carries a similar number of genes, which means human biological complexity comes overwhelmingly from how genes are regulated, spliced, and combined rather than from simply having more of them. An estimate near a hundred thousand genes reflects the popular pre-sequencing guess that has since been revised sharply downward. A figure near five hundred thousand vastly overshoots even the most generous historical estimate, and a count near two thousand undershoots into a range typical of a fairly simple single-celled organism, not a human.
Source: National Human Genome Research Institute (genome.gov): International Human Genome Sequencing Consortium describes finished human genome sequence (2004)