Answer:
According to the Law of segregation presented by Mendel, each gamete receives just one copy of every allele randomly. Normally all the cells follow the Mendelian inheritance.
In Down's syndrome, an individual gets 3 copies of a chromosome instead of the normal chromosome pair. This is also known as trisomy 21. It does not follow the law of segregation of Mendelian inheritance as it gets three instead of two.