Philadelphia Chromosome (PH)
(Philadelphia Translocation, PH and Chronic Myeloid Leukemia – CML)
Translocation is a Structural Aberration of Chromosome
Translocation is a type of structural aberration of the chromosome where a segment of chromosome gets translocated to another chromosome. There may be two types of translocation based on the nature of the exchange. They are:
(1). Homologous Translocation
(2). Heterologous Translocation
In homologous translocation, the exchange of chromosomal segments occurs between the homologous chromosomes. In heterologous translocation, the chromosomal segments are exchanged between non-homologous chromosomes. The heterologous translocation in most of the cases will be a reciprocal translocation (exchange of segments between chromosomes).
Translocation causes ‘Position Effect’
The translocation of chromosomes leads to a phenomenon in molecular genetics called the ‘Position Effect’. The position effect is the change in the expression pattern of a gene due to its current position in the chromosome. For example, a normally active gene may be converted to an inactive gene when it is translocated into a new position or vice versa.