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Chromosome 2 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 2 is the second largest human chromosome, spanning more than 242 million base pairs (the building material of DNA) and representing almost 8% of the total DNA in cells. Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 2 likely contains 1,491 genes, including those of the HOXD homeobox gene cluster.〔(Vega Homo sapiens genome browser: HoxD cluster on Chromosome 2 )〕 ==Evolution== All members of Hominidae except humans, Neanderthals, and Denisovans have 24 pairs of chromosomes. Humans have only 23 pairs of chromosomes. Human chromosome 2 is a result of an end-to-end fusion of two ancestral chromosomes.〔(Human Chromosome 2 is a fusion of two ancestral chromosomes ) by Alec MacAndrew; accessed 18 May 2006.〕〔(Evidence of Common Ancestry: Human Chromosome 2 ) (video) 2007〕 The evidence for this includes: * The correspondence of chromosome 2 to two ape chromosomes. The closest human relative, the chimpanzee, has near-identical DNA sequences to human chromosome 2, but they are found in two separate chromosomes. The same is true of the more distant gorilla and orangutan.〔(Human and Ape Chromosomes ); accessed 8 September 2007.〕 * The presence of a vestigial centromere. Normally a chromosome has just one centromere, but in chromosome 2 there are remnants of a second centromere. * The presence of vestigial telomeres. These are normally found only at the ends of a chromosome, but in chromosome 2 there are additional telomere sequences in the middle. Chromosome 2 is consistent with the common ancestry of humans and other apes. According to researcher J. W. IJdo, "We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2." 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chromosome 2 (human)」の詳細全文を読む スポンサード リンク
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