HOTAIR (for HOX transcript antisense RNA)[3] is a human gene located between HOXC11 and HOXC12 on chromosome 12. It is the first example of an RNA expressed on one chromosome that has been found to influence the transcription of the HOXD cluster posterior genes located on chromosome 2. The sequence and function of HOTAIR are different in humans and mice.[4] Sequence analysis of HOTAIR revealed that it exists in mammals, has poorly conserved sequences and considerably conserved structures, and has evolved faster than nearby HoxC genes.[5] A subsequent study identified HOTAIR has 32 nucleotides long conserved noncoding element (CNE) that has a paralogous copy in HOXD cluster region (located between HOXD11 and HOXD12),[6] suggesting that the HOTAIR conserved sequences predate whole genome duplication events at the root of vertebrate. While the conserved sequence paralogous with HOXD cluster is 32 nucleotide long, the HOTAIR sequence conserved from human to fish is about 200 nucleotide long and is marked by active enhancer features (bidirectional transcription, H3K4me1 and H3K27ac peaks).[6]