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Chromosomal Translocations

Submitted by bpmccarthy on Mon, 11/11/2019 - 16:19

A chromosomal translocation occurs when a segment of one chromosome becomes attached to another. In reciprocal translocations two non-homologous chromosomes exchange genetic material, and they arise from two different mechanisms: chromosomal breakage/DNA repair and abnormal crossovers. Reciprocal translocations lead to a rearrangement of the genetic material, not a change in the total amount thus, they are called balanced translocations. Reciprocal translocations, like inversions, are usually without phenotypic consequences. In a few cases, they can result in position effects and break point effects. In simple translocations the transfer of genetic material occurs in only one direction, these are also called unbalanced translocations. Unbalanced translocations are associated with phenotypic or even lethality, for example: Familial Down's Syndrome. In this condition, the majority of chromosome 21 is attached to chromosome 14. The affected individual would have three copies of genes found on a large segment of chromosome 21, therefore, they exhibit the characteristics of Down's Syndrome. Familial Down's Syndrome is the most common type of chromosomal rearrangement in humans and occurs Approximately 1 in 900 births.