Unformatted text preview: 85 3.2 The nature of chromosomes CENTROMERES The centromere is the region of the chromosome to which spindle fibers attach. The chro- mosome usually appears to be constricted at the cen- tromere region. The position of this constriction defines the ratio between the lengths of the two chromosome arms. This ratio is a useful characteristic for distinguish- ing chromosomes (see Table 3-3). Centromere positions are categorized as telocentric (at one end), acrocentric (off center), or metacentric (in the middle). When genomic DNA is spun for a long time in a ce- sium chloride density gradient in an ultracentrifuge, the DNA settles into one prominent visible band. However, satellite bands are often visible, distinct from the main DNA band. Such satellite DNA consists of multiple tan- dem repeats of short nucleotide sequences, stretching to as much as hundreds of kilobases in length. Probes may be prepared from such simple-sequence DNA and al- lowed to bind to partially denatured chromosomes. Thelowed to bind to partially denatured chromosomes....
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.
- Spring '08