The human genome is stored on 23 chromosome pairs in the cell nucleus and in the small mitochondrial DNA. A great deal is now known about the sequences of DNA which are on our chromosomes. What the DNA actually does is now partly known. Applying this knowledge in practice has only just begun.
The Human Genome Project (HGP) produced a reference sequence which is used worldwide in biology and medicine. Nature published the publicly funded project's report, and Science published Celera's paper. These papers described how the draft sequence was produced, and gave an analysis of the sequence. Improved drafts were announced in 2003 and 2005, filling in to ≈92% of the sequence.
The latest project ENCODE studies the way the genes are controlled.
The human genome contains just over 20,000 protein-coding genes, far fewer than had been expected. In fact, only about 1.5% of the genome codes for proteins, while the rest consists of non-coding RNA genes, regulatory sequences, and introns.
However, a single gene can produce a variety of proteins by means of RNA splicing. One particular Drosophila gene (DSCAM) can be alternatively spliced into 38,000 different mRNAs. Each mRNA codes for a different peptide chain. Therefore the number of proteins produced is far above the number of coding genes.
With RNA splicing and post-RNA translation changes, the total number of unique human proteins may be in the low millions.
The idea that most DNA is useless 'junk' is wrong. At least 80% of the genome has definite functions.
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