Telomere Expansion, Contraction and Subtelomeric Rearrangement

Telomeres are repetitive sequences of DNA at the ends of chromosomes that protect the chromosomes from degradation and allow for chromosomal shortening during replication while maintaining gene integrity at the end of the chromosome. Human telomeres, with the exception of those in human sperm, are much shorter than telomeres in non-human primates. While human telomeres are shorter overall, there are gene families within telomeric regions, such as the KIR family, that have undergone human lineage specific duplication, have unique locations in telomeres in humans, and have undergone recombination and conversion events. Subtelomeric regions lie adjacent to telomeres and contain similar genetic content to that of pericentromeric regions, including segmental duplications and bands of heterochromatin. The source of subtelomeric duplication sequences is primarily from other subtelomeric regions, and in contrast to telomere shortening, subtelomeric sequences have undergone human-specific large-scale duplication events since the Homo-Pan split. These regions are therefore major sites housing genes that have undergone human lineage-specific copy number increases and contain sequences that have dispersed in a human-specific fashion to novel regions of the genome, an example being the sequence f7501 that has a single copy in non-human primates and 7-11 copies in humans at subtelomeric locations on multiple chromosomes.