Distribution of repetitive DNA elements within Exon / Intron structures
The 13 expressed exons [numbered
dark-green units]
for a single protein-coding gene constitute a very small
portion of the total 50 Kbp region. The intervening introns
[light-green areas]
include a number of families of repetitive DNA sequences, shown separately in
the exploded views below. These include short interspersed repeats
(SINEs, including Alu
family sequences that make up about one-third of the human
genome), long interspersed repeats
(LINEs, including the L1
family), long tandem repeats
(LTRs), and simple sequence repeats (SSRs),
also called VNTRs (Variable Number of
Tandem Repeats) or micro- & mini-satellites.
Note that the SSRs are labelled as two- or
four-base motifs that are repeated n
times each.