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In genetics, chromosome translocation is a phenomenon that results in unusual rearrangement of chromosomes. This includes balanced and unbalanced translocation, with two main types: reciprocal, and Robertsonian translocation. Reciprocal translocation is a chromosome abnormality caused by exchange of parts between non-homologous chromosomes. Two ...
The chromosomal defect in the Philadelphia chromosome is a reciprocal translocation, in which parts of two chromosomes, 9 and 22, swap places. The result is that a fusion gene is created by juxtaposing the ABL1 gene on chromosome 9 (region q34) to a part of the BCR (breakpoint cluster region) gene on chromosome 22 (region q11).
This chromosome was discovered in 1960 by Peter Nowell and David Hungerford, and it is a fusion of parts of DNA from chromosome 22 and chromosome 9. The broken end of chromosome 22 contains the "BCR" gene, which fuses with a fragment of chromosome 9 that contains the " ABL1 " gene.
The cancer stem cell hypothesis proposes that the different kinds of cells in a heterogeneous tumor arise from a single cell, termed Cancer Stem Cell. Cancer stem cells may arise from transformation of adult stem cells or differentiated cells within a body. These cells persist as a subcomponent of the tumor and retain key stem cell properties.
The first fusion gene [1] was described in cancer cells in the early 1980s. The finding was based on the discovery in 1960 by Peter Nowell and David Hungerford in Philadelphia of a small abnormal marker chromosome in patients with chronic myeloid leukemia—the first consistent chromosome abnormality detected in a human malignancy, later designated the Philadelphia chromosome. [3]
A chromosome translocation occurs in patients with CML. Part of chromosome 9 breaks off and attaches itself to chromosome 22, facilitating exchange of genetic material between chromosomes 9 and 22. The rearrangement of the chromosomes changes the positions and functions of certain genes, which causes uncontrolled cell growth. [4]
This type involves myc oncogene translocation from chromosome 8 to the Ig lambda locus on chromosome 22. This type of translocation is involved in about 5% of cases of Burkitt lympohoma. The c-myc gene found on chromosome 8 is part of the MYC family of genes that serve as regulators of cellular transcription and is associated with Burkitt lymphoma.
The preparation and study of karyotypes is part of cytogenetics. The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). [4] [5] p28 Thus, in humans 2n = 46.