Class 12 NEET Biology Principles of Inheritance and Variation Questions Part 1

Nondisjunction is the failure of separation of the homologous chromosome during cell division which results in an embryo with three copies of chromosome 21 instead of the usual two. As the embryo develops, the extra chromosome is replicated in every cell of the body and this type of disorder is called as Down's syndrome or trisomy 21. Down's syndrome does not occur due to crossing over, linkage and it is not sex linked. Thus, option A is correct.