You could argue that in early succession areas species may have not been adapted or evolved. In Darwin's theory, life began in a shallow, warm pond. If that is the case, species would then venture deeper when their area they are in is suitable and having success
The four nitrogenous bases in DNA are adenine, guanine, cytosine, and thymine. They pair A-T, G-C and when transfering with RNA, A-U, which is known as Uracil, so, the pairs would be...
ATGCT
↓↓↓↓↓
UACGA
I hope this helps!