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<p><span style="font-size:16px"><span style="font-family:times new roman,times,serif">The core idea of the field of comparative genomics is that, like mentioned above, sequence, which is conserved over millions of times in distant species, implies an important biological function, and it could have been constrained by leaving several nucleotides among its own motif. It means that the conservation is not always meaning that whole base should be remained in DNA. In DNA, exons are generally well conserved between distant species in a very accurate form, thus it is easy to make a gene models. Conversely, the elements which have roles in regulation are hard to model. In that sense, the comparative genomics is very efficient. By comparing human, mouse, rat, and dog genomes, thousands of noncoding elements are analyzed which would be never possible without it.</span></span></p>