Some of this non-coding DNA is non-functional junk DNA, such as pseudogenes, but there is no firm consensus on the total amount of junk DNA. Introns make up a large percentage of non-coding DNA. It also includes promoters and their associated gene-regulatory elements, DNA playing structural and replicatory roles, such as scaffolding regions, telomeres, centromeres, and origins of replication, plus large numbers of transposable elements, inserted viral DNA, non-functional pseudogenes and simple, highly repetitive sequences. The latter is a diverse category that includes DNA coding for non-translated RNA, such as that for ribosomal RNA, transfer RNA, ribozymes, small nuclear RNAs, and several types of regulatory RNAs. Human genomes include both protein-coding DNA sequences and various types of DNA that does not encode proteins. These are usually treated separately as the nuclear genome and the mitochondrial genome. The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. The mitochondrial genome is shown to scale at bottom left. Chromosomal changes during the cell cycle are displayed at top center. This drawing shows both the female (XX) and male (XY) versions of the 23rd chromosome pair. Schematic representation of the human diploid karyotype, showing the organization of the genome into chromosomes, as well as annotated bands and sub-bands as seen on G banding.
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