Eukaryotic chromosome fine structure

Eukaryotic chromosome fine structure refers to the structure of sequences for eukaryotic chromosomes. Some fine sequences are included in more than one class, so the classification listed is not intended to be completely separate.
Chromosomal characteristics.
Some sequences are required for a properly functioning chromosome:
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.
Structural sequences.
Other sequences are used in replication or during interphase with the physical structure of the chromosome.
Protein-coding genes.
Regions of the genome with protein-coding genes include several elements:
Genes that are used as RNA.
Many regions of the DNA are transcribed with RNA as the functional form:
Other RNAs are transcribed and not translated, but have undiscovered functions.
Repeated sequences.
Repeated sequences are of two basic types: unique sequences that are repeated in one area; and repeated sequences that are interspersed throughout the genome.
Satellites.
Satellites are unique sequences that are repeated in tandem in one area. Depending on the length of the repeat, they are classified as either:
Interspersed sequences.
Interspersed sequences are nonadjacent repeats, with sequences that are found dispersed across the genome. They can be classified based on the length of the repeat as:
Both of these types are classified as retrotransposons.
Retrotransposons.
Retrotransposons are sequences in the DNA that are the result of retrotransposition of RNA. LINEs and SINEs are examples where the sequences are repeats, but there are non-repeated sequences that can also be retrotransposons.
Other sequences.
Typical eukaryotic chromosomes contain much more DNA than is classified in the categories above. The DNA may be used as spacing, or have other as-yet-unknown function. Or, they may simply be random sequences of no consequence.