Chromosome 20 spans around 66 million base pairs (the building material of DNA) and represents between 2 and 2.5 percent of the total DNA in cells.

Chromosome 20 was fully sequenced in 2001 and was reported to contain over 59 million base pairs.

[4] Since then, due to sequencing improvements and fixes, the length of chromosome 20 has been updated to just over 66 million base pairs.

Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies (for technical details, see gene prediction).

So CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes.