What Is a Translocation?

Changes in the position of chromosomal fragments are called translocations. It is accompanied by a change in gene position. When a translocation occurs within a chromosome, it is called a shift or intrachromosomal translocation . When a translocation occurs between two homologous or non-homologous chromosomes, it is called an interchromosomal translocation. ). Inter-chromosomal translocations can be divided into translocations and mutual translocations. ^[1]

One is non-mutual translocation. After a chromosome is broken, its fragment is translocated to another chromosome. If it is connected to its end, it is called end translocation. If a chromosome fragment is inserted into the middle of another chromosome arm, then This is called translocation. The other is called mutual translocation, that is, both chromosomes undergoing translocation are broken, and the fragments are exchanged with each other. ^[2]

Translocation

After the two chromosomes break, they exchange with each other without centromere fragments to form two new derived chromosomes which are translocations. Mutual translocation is a relatively common structural aberration, which can occur between chromosomes, and the frequency of newborns is about 1-2 / 1000. Mutual translocations only have a change in position. When there is no visible increase or decrease of chromosome fragments, they are called balanced translocations. It usually has no significant genetic effects. However, it is possible that a child with a balanced translocation and a child born after marriage may obtain an abnormal chromosome that results in an increase (part of trisomy) or a decrease (part of monosomy) of a certain translocation segment. And produce corresponding effects. ^[2]

Roche translocation

Robertsonian translocation is a special form of mutual translocation. The two proximal centromeres (D / D, D / G, G / G) break at or near the centromere to form two derived chromosomes. One consists of the long arms of the two, with almost all genetic material; the other consists of the short arms of the two, a small chromosome consisting of the two short arms. It is often lost due to a lack of centromeres or because it consists almost entirely of heterochromatin. Its presence does not cause phenotypic abnormalities. The Roche translocation does not cause a significant phenotype in itself, but offspring often cause miscarriages or trisomy syndromes. ^[2]