Chapter

Centromere Fissions, Complementary Isochromosomes, Telomeric Fusions, Balancing Supernumerary Chromosomes, and Jumping Translocations

R. J. McKinlay Gardner, Grant R. Sutherland and Lisa G. Shaffer

in Chromosome Abnormalities and Genetic Counseling

Fourth edition

Published on behalf of Oxford University Press

Published in print November 2011 | ISBN: 9780195375336
Published online October 2012 | e-ISBN: 9780199975174 | DOI: http://dx.doi.org/10.1093/med/9780195375336.003.0008

Series: Oxford Monographs on Medical Genetics

Centromere Fissions, Complementary Isochromosomes, Telomeric Fusions, Balancing Supernumerary Chromosomes, and Jumping Translocations

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THIS CHAPTER provides a setting for certain very rare abnormalities that cannot easily be accommodated elsewhere. Barely double-digit numbers, if that, of each category are known. Centromere fission results when a metacentric or submetacentric chromosome splits at the centromere, giving rise to two stable telocentric products. In a sense, this is the reverse of what happens in whole arm translocations. The heterozygote, a phenotypically normal individual, thus has 47 chromosomes. With the balanced complementary isochromosome carrier, two stable exactly metacentric products are generated. A balancing small supernumerary marker chromosome contains material deleted from the normal homolog. Telomeric fusion leads to a 45-chromosome count, due to the joining up of two chromosomes, tip to tip, not unlike the Robertsonian mechanism. The fusion chromosome has two centromeres, but one of these becomes inactivated. In jumping translocations, a segment can move from one chromosome to two or more recipient chromosomes. The Robertsonian fission reverses the fusion that had originally generated it.

Chapter.  2463 words.  Illustrated.

Subjects: Clinical Genetics

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