Organization of the Human genome

A 'typical' 50kbp region of the human genome is shown in the middle segment. Note that the genes make up less than half of the total region, and that large numbers of repeat sequences and non-coding intergenic DNA occur between them. In the expanded view above, there are four labelled genes, in which exons constitute only a few percent of the region, although some genes like PKP2 are exon-rich. Introns make up the bulk of the other three genes, notably SYB1. Introns in FLJ10143 and CD27 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 as 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. This might explain how humans are able to function with so few genes.

Figure ©2012 TA Brown, Introduction to Genetics (1st ed.); additional text ©2014 by Steven M. Carr