Chromosomal Bands and Sequence Features

Abstract

The linear order of DNA is preserved during chromosome condensation. Metaphase chromosome bands are clusters of contiguous replicons of 2–10 Mb that initiate and terminate DNA synthesis in synchrony during a small fraction of S phase.

Keywords: epigenetics; DNA replication; base composition; CpG islands

Figure 1.

Facultatively late‐replicating (black) X chromosome is compared with a model of late‐replicating (bold lines) and early‐replicating clusters of replicons. The adult β‐globin gene is shown for a hematopoietic cell as being located in an insulated island of early replication. (Reproduced with permission from Holmquist .)

Figure 2.

Summary of 10 different types of chromatin in mammalian genomes and their properties. T‐bands have been properly distinguished only in humans and β‐heterochromatin has been reported in only a few rodent species.

Figure 3.

GTG‐banding of a Chinese hamster cell line.

Figure 4.

Condensation of prophase bands of human chromosome 5. Early replicating bands (dark by RBG (reverse banding with BrdUrd in the last half of S phase followed by Giemsa staining)) are shown for resolutions (subscripts) ranging from 1250 to 500 bands per genome. Condensation culminates at metaphase and 350 bands per genome are shown with a GTG‐banded chromosome (right). Note that dark RBG‐bands correspond to light CTG‐bands. The T‐banded chromosome 5 (leftmost chromosome) shows that only a few R‐bands are also T‐bands. (Reproduced with permisssion from Holmquist .)

Figure 5.

Reverse ideogram of human autosomes at a resolution of 300 bands per genome with types of R‐band chromatin subdivided by their extremes of GC‐richness and Alu‐richness. Frequencies per band of 334 mapped genes (left) and 660 mapped X‐ray‐induced breaks and exchanges (right) are shown. (Reproduced with permission from Holmquist .)

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Further Reading

Bernardi G, Olofsson B, Filipski J, et al. (1985) The mosaic genome of warm‐blooded vertebrates. Science 228: 953–958.

Flickinger RA (1976) Replication‐dependent transcription in eukaryotes. International Journal of Biochemistry 7: 85–93.

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Sumner AT (1990) Chromosome Banding. London, NY: Unwin Hyman.

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Holmquist, Gerald P(Sep 2005) Chromosomal Bands and Sequence Features. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0005002]