Karyotyping human chromosomes

This picture of the human chromosomes lined up in pairs is called a karyotype. 

A ring chromosome can form when a deletion occurs on both tips of a chromosome and the remaining chromosome ends fuse together (the karyotype for a female with a ring chromosome X would be 46, r[X]). Ring chromosomes are often lost, resulting in a monosomy (e.g., loss of a ring X chromosome would produce Turner syndrome). They have been observed at least once for each human chromosome. 

Fig. 8.20. Flow karyotypes from human chromosomes (A), hamster chromosomes (B), and mouse chromosomes (C). From Gray and Cram (1990).

There has been much discussion about the potential utility of flow cytometry of chromosomes for clinical diagnosis. As regards its sensitivity, this technique appears to stand somewhere between the technique of flow analysis of whole cells for DNA content and that of microscope analysis of banded chromosomes. It may be a useful intellectual exercise for readers to ask themselves which technique or techniques would be most appropriate for detecting the following types of chromosome abnormalities (1) tetraploidy, where the normal chromosome content of cells is exactly doubled because of failure of cytokinesis after mitosis (2) an inversion in an arm of one particular chromosome and (3) trisomy (the existence of cells with three instead of two) of one of the small chromosomes. In addition to these limitations, the use of flow cytometry to look for abnormal chromosomes has been confounded by the fact that several human chromosomes are highly polymorphic, and flow karyotypes, therefore, vary considerably among normal individuals. 

Figure 1-3. Partial karyotypes of Giemsa-stained human chromosomes showing various manifestations of the fragile X site (arrows) a chromatid break (a), an isochromatid gap (b), a chromosome break (c), and endoreduplication (d).

Fig. 2.4 Chromosome analysis of the heterohybri-doma CB03. GTG banding (upper left), spectral karyotype analysis (upper right) and identification of human chromosomes by hybridization with specifically labeled human chromosome libraries...

Caspersson T., Castleman K.R., Lomakka G., Modest E.J., Moller A., Nathan R., Wall R.J., Zech L. (1971). Automatic karyotyping of quinacrine mustard stained human chromosomes. Exp. Cell Res. 67 233-235. 

Schrock E, du Manoir S, Veldman T et al (1996) Multicolor spectral karyotyping of human chromosomes. Science 273 494-497... 

Figure 36-6. A human karyotype (of a man with a normal 46,XY constitution), in which the metaphase chromosomes have been stained by the Giemsa method and aligned according to the Paris Convention. (Courtesy of H Lawce and F Conte.)...

Right The human karyotype/ a full set of chromosomes numbered according to size and content and showing characteristic banding patterns. The 22 autosomes plus either an X or Y chromosome make up the haploid set which, for the female, contains - 3,500 Mbp of DNA. Each diploid cell contains 46 chromosomes. From Alberts et at. 

Figure 19.2 A human somatic cell contains two sets of homologous chromosomes, which may be divided into two types autosomes and sex chromosomes. Autosomes are further divided into seven groups A-G. During the metaphase of cell division, each chromosome has been duplicated. Therefore, this karyotype consists of 92 chromosomes.

Identification of chromosomes (human as well as mouse and hamster) Determination of ploidy Detection and characterization of aneuploidy Gene mapping localization of specific DNA sequences Gene mapping detection of heteromorphisms and determination of parental origin of heteromorphisms Detection of gene mutations Characterization of structural aberrations Identification of marker chromosomes Characterization of tumor cells Chromosome and karyotype evolution Spatial topography of chromosomes... 

The answer is d. (Murray, pp 812—828. Scriver, pp 3-45. Sack, pp 57-84. Wilson, pp 123—148.) The case described represents one of the more common chromosomal causes of reproductive failure. Turner mosaicism. Turner s syndrome represents a pattern of anomalies including short stature, heart defects, and infertility. Turner s syndrome is often associated with a 45,X karyotype (monosomy X) in females, but mosaicism (i.e., two or more cell lines with different karyotypes in the same individual) is common. However, chimerism (i.e., two cell lines in an individual arising from different zygotes, such as fraternal twins who do not separate) is extremely rare. Trisomy refers to three copies of one chromosome, euploidy to a normal chromosome number, and monoploidy to one set of chromosomes (haploidy in humans). 

The third observation that supported a central role for DNA in cancer came from the study of chromosomes in human leukemia cells. Karyotyping is a cytological technique used to characterize the gross structure of chromosomes in mitotic cells. Researchers noticed that in cells from one type of leukemia, chronic myelogenous leukemia, there was almost always a chromosome rearrangement between chromosomes 9 and 22. This reciprocal translocation led to identification of a small 22 9 chromosome which came to be called the Philadelphia chromosome because it was discovered at the Wistar Institute in Philadelphia. Importantly, the karyotype of nonleukemic cells from patients with this form of leukemia is normal. 

Karyotype A visual display of metaphase chromosomes from somatic cells which collectively represents the chromosomal makeup of an individual a normal human karyotype is 44 autosomes (2 each of 22) and 2 sex chromosomes. 

Figure 7.12. Identification of the GC-poorcst and the GC-richest diroittosomal bands. Human karyotype at a resolution of 850 bands showing the chromosomal bands containing the GC-pooresl (LT, blue bars) and the GC-richest isochores (I l.l. red bars). 1 he 115 R bands are in white. The grey scale of the G bands is according lo Francke (1994). (Modified front Federico el a I,. 2000).

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