Which chromosomal defect is caused when part of a chromosome breaks off and reattaches backward on the same chromosome?
1. inversion
2. translocation
3. deletion
4. insertion

The right answer is an inversion.

A chromosomal inversion defines the turning on itself of a part of a chromosome during a mutation. It's often a paracentric inversion. A pericentric inversion is when the inverted segment contains the centromere.

An inversion occurred by two steps: deletion of the segment, then a backward insertion of the same segment.