Which type of DNA is a non-canonical structure that forms when a single-stranded DNA molecule folds back on itself and forms base pairs with itself?
A-DNA
B-DNA
Z-DNA
H-DNA
H-DNA is a non-canonical structure that forms when a single-stranded DNA molecule folds back on itself and forms base pairs with itself. It can be involved in genetic recombination and is implicated in certain diseases, such as Huntington's disease. Hence, option 4 is the correct answer.