Repetitive DNA sequences do occur and do cause problems. https://en.m.wikipedia.org/wiki/Trinucleotide_repeat_expansion https://en.m.wikipedia.org/wiki/Trinucl

Repetitive DNA sequences do occur and do cause problems. https://en.m.wikipedia.org/wiki/Trinucleotide_repeat_expansion https://en.m.wikipedia.org/wiki/Trinucleotide_repeat_expansi... TLDR: DNA triplet repeat expansions cause diseases like Huntington's disease.