Karyotype Interpretation

Abstract

The construction of karyotypes from human metaphase chromosomes allows for the identification of cytogenetic abnormalities at a whole genome perspective. Constitutional and acquired chromosome changes can be detected by routine and high‐resolution cytogenetic preparations, and a specific nomenclature allows for accurate communication, interpretation and reporting.

Keywords: cytogenetics; chromosomes; aneuploidy; translocation; nomenclature

Figure 1.

Normal male karyotype stained with trypsin–Giesma, resulting in G banding.

Figure 2.

Ideogram of chromosome 18, drawn at a haploid resolution of 550 bands. The centromere is filled with a hatched pattern and is designated as p11.1 and q11.1.

Figure 3.

Diagram showing meiotic nondisjunction at meiosis I (MI, left) and meiosis II (MII, right). In nondisjunction at meiosis I (left), the homologous chromosomes fail to separate and move to the same daughter cell. In the subsequent division, meiosis II, sister chromatids separate in the two daughter cells. The result is four abnormal cells: two disomic and two nullisomic. Fertilization of the disomic gametes would result in trisomy. Fertilization of the nullisomic gametes would result in monosomy. In nondisjunction at meiosis II (right), the homologous chromosomes separate properly in meiosis I, but sister chromatids fail to separate in meiosis II. This results in two normal gametes and two abnormal gametes, one disomic and one nullisomic. Fertilization of the disomic gamete or the nullisomic gamete would result in trisomic or monosomic conceptuses respectively.

Figure 4.

Diagram of mosaicism. A pair of homologous chromosomes (shaded and hatched) are shown. Mitotic nondisjunction is the failure of sister chromatids to separate (shown in the shaded chromosome), and results in a cell line that is trisomic (upper cell line) and a cell line that is monosomic (lower cell line) for the same chromosome. The survival of each cell line determines the proportion of each cell population seen in the individual.

Figure 5.

Diagrams of various chromosomal rearrangements and mechanisms of formation: (a) reciprocal translocation; (b) Robertsonian translocation; (c) isochromosome formation; (d) interstitial deletion and reciprocal duplication of a chromosomal segment; (e) terminal deletion; (f) insertion; (g) pericentric inversion (left) and paracentric inversion (right); (h) replication of ring chromosomes resulting in two ring chromosomes (top) or dicentric ring chromosomes and further rearrangement (bottom).

Figure 6.

Nonallelic, unequal crossing over through low copy repeat (LCR) DNA sequences results in reciprocal interstitial deletion and duplication chromosomes.

close

References

Flint J, Craddock CF, Villegas A, et al. (1994) Healing of broken human chromosomes by the addition of telomeric repeats. American Journal of Human Genetics 55: 505–512.

Hamerton JL, Canning N, Ray M and Smith S (1975) A cytogenetic survey of 14,069 newborn infants. I. Incidence of chromosome abnormalities. Clinical Genetics 8: 223–243.

Kaiser P (1988) Pericentric inversions: their problems and clinical significance. In: Daniel A (ed.) The Cytogenetics of Mammalian Autosomal Rearrangements, p. 163. New York, NY: Alan R Liss.

Koehler KE, Hawley RS, Sherman S, Hassold T (1996) Recombination and nondisjunction in humans and flies. Human Molecular Genetics 5: 1495–1504.

Madan K (1988) Paracentric inversions and their clinical implications. In: Daniel A (ed.) The Cytogenetics of Mammalian Autosomal Rearrangements, p. 249. New York, NY: Alan R Liss.

Mitelman F (ed.) (1991) ISCN(1991): Guidelines for Cancer Cytogenetics, Supplement to an International System for Human Cytogenetics Nomenclature. Basel: Karger.

Mitelman F (ed.) (1995) ISCN(1995): An International System for Human Cytogenetics Nomenclature. Basel: Karger.

Shaffer LG, Jackson‐Cook CK, Meyer JM, Brown JA and Spence JE (1991) A molecular genetic approach to the identification of isochromosomes of chromosome 21. Human Genetics 86: 375–382.

Shaffer LG and Lupski JR (2000) Molecular mechanisms for constitutional chromosomal rearrangements in humans. Annual Review of Genetics 34: 297–329.

Stene J and Stengel‐Rutkowski S (1988) Genetic risks of familial reciprocal and Robertsonian translocation carriers. In: Daniel A (ed.) The Cytogenetics of Mammalian Autosomal Rearrangements, p. 3. New York, NY: Alan R Liss.

Therman E, Susman B and Deniston C (1989) The nonrandom participation of human acrocentric chromosomes in Robertsonian translocations. Annals of Human Genetics 53: 49–65.

Further Reading

Heim S and Mitelman F (1995) Cancer Cytogenetics. Chromosomal and Molecular Genetic Aberrations of Tumor Cells. New York, NY: Wiley‐Liss.

Rieger R, Michaelis A and Green MM (1976) Glossary of Genetics and Cytogenetics. New York, NY: Springer.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Shaffer, Lisa G(Jan 2006) Karyotype Interpretation. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0005778]