Examples of a structural variation include a large deletion, insertion, duplication and inversion. Each requires the DNA duplex to be broken and rejoined, and this creates a new sequence of bases at the rejoined sites, i.e. the breakpoints.

Sequencing the new breakpoint regions is a good way (perhaps the only way?) to demonstrate an inversion, which does not increase or decrease the amount of DNA.

Original sequence: 123456789

Sequence with inversion: 123765489

Breakpoint sequences are at 37 and 48