Are all genetic instructions in DNA?
Genetic information is the heritable information used by organisms to guide their self-assembly. It's why traits can persist across generations. DNA is, by far, the primary material used (by life) to encode genetic information, but it's not the only one. RNA is a pretty common alternative to DNA.

If we're looking to Wikipedia, this is actually referred to (in passing) on many pages about genetics. They usually link to the page on the best known edge case, RNA viruses:


  An RNA virus is a virus that has RNA (ribonucleic acid) as its genetic material. This nucleic acid is usually single-stranded RNA (ssRNA) but may be double-stranded RNA (dsRNA). Notable human diseases caused by RNA viruses include Ebola hemorrhoragic fever, SARS, influenza, hepatitis C, West Nile fever, polio, and measles.


While viruses fall into a weird middle ground between life and inanimacy, they still all need genes, and many of them use RNA for that. Side note: retroviruses get their name from the fact that they use reverse transcription to synthesize DNA from an RNA template.