Assertion (A): Cri-du-chat syndrome is an intrachromosomal aberration. Reason (R): It is caused in humans by deletion of a part of short arm of chromosome 5.

In the following question there are two statements, Assertion (A) and Reason (R), consider both the statements independently and mark your answers as under:
1. If A and R both are correct and R is correct explanation of A.
2. If A and R both are correct and R is not correct explanation of A.
3. If A is correct and R is incorrect.
4. If A is incorrect and R is correct.
5. If A and R both are incorrect.

Both Assertion (A) and Reason (R) statements are correct, and R is correct explanation of A. In chromosomal aberration there is an alteration in the structural organisation of chromosome.  Aberrations are of two types, Intrachromosomal aberration :  when the alteration is within single chromosome. Interchromosomal aberration : when alteration involves the intervention of two or more chromosomes. Cri-du-chat syndrome in humans is caused by deletion of a part of short arm of chromosome 5. It involves alteration in only one chromosome; hence it is an intrachromosomal aberration.