Translocation
- Mutual exchange (reciprocal) of the chromosome segments between non homologous chromosome.
- An exchange of parts between two non homologous chromosomes is called reciprocal translocation.
- In simple translocation a segment of one chromosome breaks and is transferred to another non-homologous chromosome.
Translocations in human beings
• Certain types of cancer are associated with chromosome rearrangements.
• Two examples of tumours associated with consistent chromosome translocations are Chronic Myelogenous Leukaemia (CML) and burkitt’s lymphoma.
• Two examples of tumours associated with consistent chromosome translocations are Chronic Myelogenous Leukaemia (CML) and burkitt’s lymphoma.
(1) Chronic Myelogenous Leukaemia (CML)
• Chronic myelogenous leukaemia in human beings is a fatal
cancer involving uncontrolled replication of myeloblasts (stem cells of
white blood cells).
• Ninety percent of CML is associated with an aberration of chromosome 22.
• This abnormal chromosome was originally discovered in the city of Philadelphia in 1959 and thus is called the ‘Philadelphia chromosome’.
• Initially it was though to have a simple deletion in its long arm, however, subsequent analysis using molecular techniques has shown that the Philadelphia chromosome is actually the result of a reciprocal translocation between chromosomes 9 and 22.
• In the Philadelphia translocation, the tip of the long arm of chromosome 9 has been joined to the body of chromosome 22 and the distal portion of the long arm of chromosome 22 has been joined to the body of chromosome 9.
• CML is characterized by an excess of granular leucocytes in the blood.
• With the increase in the number of leucocytes, there is a reduction in the number of RBCs resulting in severe anaemia.
• Ninety percent of CML is associated with an aberration of chromosome 22.
• This abnormal chromosome was originally discovered in the city of Philadelphia in 1959 and thus is called the ‘Philadelphia chromosome’.
• Initially it was though to have a simple deletion in its long arm, however, subsequent analysis using molecular techniques has shown that the Philadelphia chromosome is actually the result of a reciprocal translocation between chromosomes 9 and 22.
• In the Philadelphia translocation, the tip of the long arm of chromosome 9 has been joined to the body of chromosome 22 and the distal portion of the long arm of chromosome 22 has been joined to the body of chromosome 9.
• CML is characterized by an excess of granular leucocytes in the blood.
• With the increase in the number of leucocytes, there is a reduction in the number of RBCs resulting in severe anaemia.
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