1 Set of hunches. 2  If a theory is a set of hunches, it means we arenât yet sure we have the answer. 3  Theories always involve an element of speculation or conjecture. 4  A theory is not just one inspired thought or an isolated idea.  A theory offers some sort of explanation.
Uracil is paired with thymine in RNA and it is paired with Adenine in DNA. In DNA transcription (from DNA to RNA), uracil pairs with adenine. in regular DNA replication adenine pairs with thymine.
Accidental deamination may change the cytosine to uracil, or the methylated cytosine to thymine. Cytosine is one of four bases in DNA molecules. As shown in the above figure, it may be mutated to uracil by deamination. Since uracil is not part of DNA, this mutation can easily be detected and repaired by base excision. Suppose DNA, like RNA, were made up of uracil, then the cytosine to uracil mutation could be corrected only by mismatch repair which is very inefficient.