Some genetic diseases cannot be diagnosed by changes in restriction sites. Some of these can be detected by allele-specific oligonucleotide probes. These are

• A. copies of the gene with an altered sequence so that a restriction site is inserted
• B. mutagenized copies of a gene
• C. short sequences that will hybridize only to a specific base sequence
• D. PCR-amplified variable numbers of tandem repeats (VNTRs)