The human genome consists of 20-25,000 genes, making up about 2% of the human DNA. Large non-coding regions of DNA called introns are spliced from pre-mRNA in the nucleus before it leaves through the nuclear pores. The exons that are spliced together are then translated in the cytoplasm. Other non-coding regions of DNA are telomeres at the ends and centromeres with which chromosomes attach to the spindle during nuclear division.Within the non-coding regions are short repeating sequences known as satellites. 20-50 base pair minisatellites are repeated hundreds of times at up to 1000 locations, 2-4 base pair microsatellites (short tandem repeats) are repeated up to 15 times and are always in the same position on chromosomes.