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A 21st chromosome trisomy
Trisomy is the presence of one chromosome in triplicate (2N+1). Trisomy of the 21 st chromosome causes Down's Syndrome (45+XY/45+XX).
It is characterized by round face, broad forehead and palmer crease with low intelligence. The 18th chromosome trisomy (45+XY/45+XX) causes Edward's Syndrome characterized by small jaws and mouth, deformed ear, etc.
The 22nd chromosome trisomy results in spontaneous abortion during the first trimester of pregnancy.
Sex linked disorder are the one for which the governing genes are present on the sex chromosomes, e.g., are hemophilia, colour blindness etc.