Down’s syndrome is caused due to the presence of the additional copy of the 21st chromosome caused due to nondisjunction, i.e., the failure of separation of the sister chromatids during cell division. Therefore it is also called as the trisomy of 21. It is represented as 47, XX/XY.
Turner’s syndrome is caused due to the absence of one of the X chromosomes in females arising due to nondisjunction of X chromosomes during the ovum formation. It is represented as 45, XO.
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