Organization of the Human genome

A 'typical' 50kbp region of the human genome is shown in the middle segment, with putative gene regions expanded above. Exons constitute only a few percent of the region. Introns make up the bulk of gene regions, and along with intergenic regions are interuppted by repeat sequences (cf. locus FLJ10143). Many of the these dispersed repeats are members of the Alu family, a 200~300 bp repeat dispersed many hundreds of thousands of times across the genome. Although repetitive DNA is sometimes referred to as "junk DNA", this probably represents the current state of unknowledge. For example, it appears likely that repetitive elements assist in alternative splicing of exons to produce different transcripts with different properties from the same coding region, which might explain how humans are able to function with so few genes..

Figure 2012 TA Brown, Introduction to Genetics (1st ed.); additional text 2013 by Steven M. Carr