How would dna extracted from an onion be different from dna extraction from cauliflower?

Dna extration from a onion and from a cauliflower would be different because even though all DNA is composed by the same nucleotides (A, T, C and G), the sequence of their genes will be different. That difference is why a cauliflower doesn't look like a onion. The cauliflower has genes that, when expressed, make the organism look like cauliflower and nothing else ...