“We read DNA using the letters C,A,G and T” should be “We read DNA using the letters C, A, G and T”.

“They have 7 differences, and therefore the Hamming Distance is 7.” could probably be “They have 7 differences, therefore the Hamming Distance is 7” since therefore is an conjunctive adverb. I’d rather fix the C,A,G and T spacing though.

The text uses both Hamming Distance and Hamming distance in a few spots so it’d be good to be consistent throughout. Hamming distance - Wikipedia uses Hamming distance so I’d favor that casing personally.