Interviewee: Matt Ridley. The second largest human chromosome, chromosome 2, was formed from the fusion of two medium-sized chromosomes. This fusion occurred in our ancient human ancestors. Although the content of our DNA is only 2% different from our closest primate relatives, this gross mutation makes us genetically distinct. Until 1955, it was thought that people, like apes, had 24 pairs of chromosomes. (DNAi Location: Genome > Tour > Genome spots > Chromosome 2: being human > A chromosome 2 story)

Our genes are very similar to those of chimpanzees. The difference is probably only 1.5% of our DNA. But there is one obvious difference: chimpanzees have 24 pairs of chromosomes, we have 23 pairs. And the reason is because two smaller ape chromosomes have come together and fused in human beings. And that's what forms chromosome 2, the second largest of our chromosomes. Now this difference, this fusing of the chromosomes, may have been one of the events that led us to separate from the chimpanzee lineage. The differences between us and chimpanzees might turn out to be mainly ones of the timing of developmental genes – the switching on and off of genes during development – rather than gross differences in the genes themselves.

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