Robertsonian translocation

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Robertsonian translocations are restricted to acrocentric chromosomes only (of which there are five different ones: chromosomes 13,14,15,21, and 22) and these acrocentric chromosomes are characterised by short (p) arms which mainly consist of genes which transcribe for ribosomal RNA[1].

This type of translocation occurs when the long (q) arm of the chromosome fuses with another q arm from a non-homologous chromosome. The p arms are lost and so is one centromere. As a result the end karyotype has 45 chromosomes in total.

If this translocation occurs in somatic cells, then the phenotype is normal. This is not the case for germ line cells. Carriers of Robertsonian translocations have unaffected phenotypes but can produce unbalanced gametes[2].

Consequently, Robertsonian translocations can result in both monosomies and trisomies. The former are likely to result in spontaneous abortions, whilst the latter can result in syndromes such as Down Syndrome, caused by a trisomy of chromosome 21[3].

References

  1. University of Illinois. CHROMOSOMAL INHERITANCE. Availabe at: https://www.uic.edu/classes/bms/bms655/lesson9.html [Accessed 03/12/2015].
  2. Venkateshwari A, Srilekha A, Sunitha T, Pratibha N, Jyothy A. A Robertsonian Translocation rob (14;15) (q10:q10) in a Patient with Recurrent Abortions. J Reprod Infertil. 2010;11(3):197–200.
  3. University of Illinois. CHROMOSOMAL INHERITANCE. Availabe at: https://www.uic.edu/classes/bms/bms655/lesson9.html [Accessed 03/12/2015].

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