Complex sentence: Compared to any other group of tetrapods, birds are the ones that have less repeated elements in their genomes, comprising only 4-10% of its extent, a rather small number when compared to the 34-52% that they take up in mammals.
Split into simpler sentences: Compared to any other group of tetrapods, birds are the ones that have less repeated elements in their genomes, comprising only 4-10% of its extension. A rather small number when compared to the 34-52% that they take up in mammals.