Final answer:
Next-generation sequencing (NGS) is the most useful FISH technique for detection of multiple complex genomic mutations.
Step-by-step explanation:
The most useful FISH technique for detection of multiple complex genomic mutations is Next-generation sequencing (NGS). NGS is a high-throughput sequencing technology that enables the simultaneous sequencing of millions of DNA fragments.
It can detect a wide range of mutations, including single nucleotide variants, insertions, deletions, and structural variations. NGS is particularly useful for studying complex genomic disorders where multiple mutations are involved.