1. Translocation of the long arm of chromosome 21 to the short arm of chromosome
ID: 35662 • Letter: 1
Question
1. Translocation of the long arm of chromosome 21 to the short arm of chromosome 14 with the retention of the chromosome 14 centromere. Asssume a break in the short arm of chromosome 14 at region 1, band 1, and the loss of the entire short arm of 21.
The chromosome resulting form this translocation is properly referred to as a ___________ chromosome.
2. Studies in recent years have shown that a number of forms of cancer are associated wit hspecific structural chromosome abberations. For example, chronic myelogenous leukemia (CML) is associated with the so-called Philadelphia chromosome (Ph). The defective chromosomes in CML occur only in white blood cells and involve a reciprocal tanslocation (exchange of segments) beterrn the long arms of chromosomes 9 and 22. Careful sgtudies indicate that the chromosome breaks onnur in the long arms of chromosome 9 (region 3, band 4) and 22 (region 1, band 1). Use propersymbolism to designate the resulting derivative chromosomes.
Explanation / Answer
1. the D and G group chromosomes.
2. The chromosomal defect seen in the Philadelphia chromosome is the result of reciprocal translocation, where parts of two different chromosomes, chromosome 9 and chromosome 22, swap places with each other.
The result of the swap or exchange of places by the two chromosomes is that a fusion gene is created by juxtapositioning the Abl1 gene on chromosome 9 (region q34) to a part of the BCR ("breakpoint cluster region") gene on chromosome 22 (region q11). This is a reciprocal translocation, creating an unusually long chromosome 9 which is termed as a derivative chromosome, or der 9 chromosome, and the chromosome 22 is a truncated chromosome 22 also known as the Philadelphia chromosome. In agreement with the International System for Human Cytogenetic Nomenclature (ISCN), this chromosomal translocation is designated as t(9;22)(q34;q11). where Abl stands for "Abelson", the name of a leukemia virus which carries a similar protein.
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