Chromosomal Characteristics
Some sequences are required for a properly functioning chromosome:
- Centromere: Used during cell division as the attachment point for the spindle fibers.
- Telomere: Used to maintain chromosomal integrity by capping off the ends of the linear chromosomes. This region is a microsatellite, but its function is more specific than a simple tandem repeat.
Throughout the eukaryotic kingdom, the overall structure of chromosome ends is conserved and is characterized by the telomeric tract - a series of short G-rich repeats. This is succeeded by an extensive subtelomeric region consisting of various types and lengths of repeats - the telomere associated sequences (TAS). These regions are generally low in gene density, low in transcription, low in recombination, late replicating, are involved in protecting the end from degradation and end-to-end fusions and in completing replication. The subtelomeric repeats can rescue chromosome ends when telomerase fails, buffer subtelomerically located genes against transcriptional silencing and protect the genome from deleterious rearrangements due to ectopic recombination. They may also be involved in fillers for increasing chromosome size to some minimum threshold level necessary for chromosome stability; act as barriers against transcriptional silencing; provide a location for the adaptive amplification of genes; and be involved in secondary mechanism of telomere maintenance via recombination when telomerase activity is absent.
Read more about this topic: Eukaryotic Chromosome Fine Structure