Diseases From Altered Chromosomes: Cri Du Chat and Chronic Myelogenous Leukemia


The cancerous cells in nearly all CML patients contain an abnormally short chromosome 22, the so-called Philadelphia chromosome, and an abnormally long chromosome 9. These altered chromosomes result from the reciprocal translocation shown here, which presumably occurred in a single white blood cell precursor undergoing mitosis and was then passed along to all descendant cells.
Source: Urry, Lisa A.. Campbell Biology (p. 309). Pearson Education. Kindle Edition.

Campbell Biology

Many deletions in human chromosomes, even in a heterozygous state, cause severe problems. One such syndrome, known as cri du chat (“cry of the cat”), results from a specific deletion in chromosome 5. A child born with this deletion is severely intellectually disabled, has a small head with unusual facial features, and has a cry that sounds like the mewing of a distressed cat. Such individuals usually die in infancy or early childhood.

Chromosomal translocations can also occur during mitosis; some have been implicated in certain cancers, including chronic myelogenous leukemia (CML). This disease occurs when a reciprocal translocation happens during mitosis of cells that are precursors of white blood cells. The exchange of a large portion of chromosome 22 with a small fragment from a tip of chromosome 9 produces a much shortened, easily recognized chromosome 22, called the Philadelphia chromosome. Such an exchange causes cancer by creating a new “fused” gene that leads to uncontrolled cell cycle progression.


Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html


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