A Down syndrome child is mentally retarded. All cytogenetic abnormalities may occur except?
a. Deleted chromosome 21(Ref: Nelson's 20/e p 610-615, Ghai 8/e p 637-639)An extra copy of chr 21 is required to cause trisomy 21 (Down syndrome), so deletion of chr 21 will not cause it.
Deleted chromosome 21
Trisomy 21
Robertsonian translocation
Mosaic
Genetics And Genetic Disorders