Organization of repetitive DNA elements between genes
Protein-coding genes comprise both expressed exons (dark green) and
intervening introns (light
grey regions). Repetitive
DNA elements may be interspersed both within and between genes. The
latter include short or long interspersed elements (SINEs and LINEs), and regions with variable
numbers of tandem repeats (VNTRs: micro- & minisatellites).
Other repetitive elements found between
coding genes include centromeric heterochromatin,
which are genetically inert regions near the chromosomal
centromeres that serve as an attachment point for
microspindles during mitosis and meiosis, and Nucleolus-Organizing Regions
(NORs),
which comprise tandem
repeats of rDNA genes
on particular chromosomes. Centromeres
and NORs are
frequently detectable cytologically.