subtelomere

Subtelomere is the region of a eukaryotic chromosome located immediately proximal to the telomere. It lies between the telomeric repeats at the chromosome end and the more internally located euchromatin, and its exact length and composition vary among chromosomes and species. In many organisms the subtelomeric zone contains a mosaic of repetitive sequences and segmental duplications, along with lineage- or species-specific genes that can be highly dynamic.

The subtelomere is typically rich in structural variation and recombination activity. Its repetitive content and propensity for rearrangements contribute to rapid evolution of gene content, leading to expanded gene families or copy-number differences between individuals. This region often shows distinct chromatin organization and can participate in telomere position effects, influencing the expression of nearby genes.

Biological significance varies by organism. In humans, subtelomeres harbor blocks of duplicated sequences and genes that differ in copy number between chromosomes and individuals, contributing to genome diversity. In yeast such as Saccharomyces cerevisiae, subtelomeres contain gene families like FLO and PAU that are prone to expansion and diversification. In the malaria parasite Plasmodium falciparum, subtelomeric regions host var gene families that drive antigenic variation and immune evasion.

Overall, subtelomeres are dynamic chromosome regions at the frontier between telomere biology and the rest of the genome, shaping genetic diversity, genome stability, and gene regulation across diverse eukaryotes.