Edward syndrome is on account of .......

Down's syndrome is an example of

Relative morphologies of chromosomes of an individual indicate his/her

If a female individual has a small round head,furrowed tongue,partially open mouth,and a broad palm with a characteristic palm crease,and also exhibits retarded physical,psychomotor,and mental development,the karyotype analysis of such an individual will show:

Which one of the following conditions in humans is correctly matched with its chromosomal abnormality/linkage?

Three copies of chromosome-$21$ in a child with Down's syndrome have been analysed using molecular biology technology to detect any possible $DNA$ polymorphism with reference to different alleles located on chromosome-$21$. Results showed that out of $3$ copies,$2$ of the chromosomes of the child contain the same alleles as one of the mother's alleles. Based on this,when did the non-disjunction event most likely occur?