Chromosomal Banding - Research Article from Macmillan Science Library: Genetics

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Chromosome Structure

To understand what chromosomal bands represent, it is helpful to understand the structure of chromosomes. Eukaryotic chromosomes are composed of chromatin, a combination of nuclear DNA and proteins. At metaphase, which is a phase in the cell cycle after the DNA in the nucleus has been replicated, each chromosome contains two identical strands of DNA. (Each strand contains two complementary strands of nucleotides.) The two strands of DNA, or chromatids, are arranged in a double-helix and are held together at a single point, the centromere, or primary constriction point.

C-banded metaphase cell. C-banded metaphase cell.

During mitosis, each chromatid becomes condensed approximately ten-thousand fold reaching maximal condensation at metaphase. DNA that was roughly 5 centimeters (2 inches) long is compacted to 5 micrometers. The DNA wraps around proteins called histones, forming complexes called nucleosomes. The nucleosomes twist around each other and assume a loop formation projecting out from the chromosome's protein backbone...

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This section contains 1,249 words
(approx. 5 pages at 300 words per page)
Buy the Chromosomal Banding Encyclopedia Article
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Macmillan Science Library: Genetics
Chromosomal Banding from Macmillan Science Library: Genetics. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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