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Duplications near Telomeres

 

b, Sequence organization in human subtelomeric DNA

regions. The terminal repeat tract consists of 2–15 kb of simple repeat sequence

(TTAGGG)n and is indicated by the black arrow at right. Short (50–250 bp) and often

degenerate (TTAGGG) tracts (internal black arrows) are highly enriched (.25-fold) in

subtelomeric DNA relative to elsewhere in the genome. A subtelomeric repeat (Srpt)

region (blue) consists of a mosaic patchwork of segmentally duplicated DNA tracts that

occur in two or more subtelomere regions and range in size from ,10 kb to .300 kb.

TAR1, D4Z4 and beta satellite sequences are frequently associated with Srpt regions.

Proximal to the Srpt region is chromosome-specific genomic DNA, typically with a high GC

content and high gene density. Stretches of segmentally duplicated DNA that occur only

once within subtelomeric regions (tan) are interspersed with 1-copy subtelomeric DNA

(yellow) in a telomere-specific fashion. Overall, segmentally duplicated DNA comprises

approximately 25% of the most telomeric 500 kb of the chromosome, a fivefold

enrichment over the genome-wide average.