Robertsonian translocations are a common form of chromosomal rearrangement, which occurs in the five acrocentric human chromosome pairs, namely 13, 14, 15, 21, and 22. They are named for the American insect geneticist W. R. B. Robertson, who first described a Robertsonian translocation in grasshoppers in 1916. They are also called whole-arm translocations or centric-fusion translocations. They are a type of chromosomal translocation.

One in 900 humans is born with a Robertsonian translocation. The most frequent forms of Robertsonian translocations are between chromosomes 13 and 14, 13 and 21, and 21 and 22, and occur when the long arms of two acrocentric chromosomes fuse at the centromere and the two short arms are lost.

A Robertsonian translocation in balanced form results in no excess or deficit of genetic material and causes no health difficulties. In unbalanced forms, Robertsonian translocations cause chromosomal deletions or addition and result in syndromes of multiple malformations, including trisomy 13 (Patau syndrome) and trisomy 21 (Down syndrome).

A Robertsonian translocation results when the long arms of two acrocentric chromosomes fuse at the centromere and the two short arms are lost. In this case, the long arms of chromosomes 13 and 14 have fused, but no genetic material was lost - this person is completely normal despite the translocation. Common Robertsonian translocations are confined to the acrocentric chromosomes 13, 14, 15, 21 and 22, because the short arms of these chromosomes contain no essential genetic material.

People with Robertsonian translocations have only 45 chromosomes in each of their cells, yet all essential genetic material is present, and they appear normal. Their children, however, may either be normal and carry the fusion chromosome (depending which chromosome is represented in the gamete), or they may inherit a missing or extra long arm of an acrocentric chromosome. Genetic counseling and genetic testing is offered to families that may be carriers of chromosomal translocations.

See also

• Chromosomal translocation

Reference

• Robertson WRB. Chromosome studies. I. Taxonomic relationships shown in the chromosomes of Tettigidae and Acrididae. V-shaped chromosomes and their significance in Acrididae, Locustidae and Gryllidae: chromosome and variation. J Morph 1916;27:179-331.