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Genomes and Maps module of the MLA course on
Introduction to Molecular Biology Information Resources
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Cytogenetic Bands


Each human chromosome has a short arm ("p" for "petit") and long arm ("q" for "queue"), separated by a centromere. The ends of the chromosome are called telomeres.

Each chromosome arm is divided into regions, or cytogenetic bands, that can be seen using a microscope and special stains. The cytogenetic bands are labeled p1, p2, p3,   q1, q2, q3, etc., counting from the centromere out toward the telomeres. At higher resolutions, sub-bands can be seen within the bands. The sub-bands are also numbered from the centromere out toward the telomere.

For example, the cytogenetic map location of the CFTR gene is 7q31.2, which indicates it is on chromosome 7, q arm, band 3, sub-band 1, and sub-sub-band 2.

The ends of the chromosomes are labeled ptel and qtel. For example, the notation 7qtel refers to the end of the long arm of chromosome 7.

For more information on chromosome banding and chromosome nomenclature, see pp. 37-39 of:

Strachan, T. and Read, A.P. 1999. Human Molecular Genetics, 2nd ed. New York: John Wiley & Sons.

Genomes and Maps
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Revised 11/07/2007