TRANSLOCATIONS
Reciprocal translocation involves any 2 or more nonhomologous
chromosomes and occurs when there is a breakage and reunion of portions
of the involved chromosomes to yield new products. Carriers of balanced
reciprocal translocations have 46 chromosomes, with both derivative
chromosomes present. Offspring may also have 46 chromosomes but only one
of the derivative chromosomes is present.
Robertsonian translocation always involves the acrocentric
chromosomes and is caused by centric fusion after loss of the satellite region
of the short arms of the original acrosomic chromosome. The karyotype of a
balanced Robertsonian translocation will appear to have only 45
chromosomes; however, the full complement of genetic material is present,
and there are no clinical effects. The offspring may have 46 chromosomes but
have double the genetic material of a particular chromosome.