<em>Replication is a process involving the production of daughter copy by DNA. Transcription, on the other hand, is a process during which the coding strand of DNA is used as a template for the production of mRNA - messenger RNA.</em>
During DNA replication, <u>Adenine is paired with Thymine while Guanine is paired with Cytosine</u>. During transcription, <u>Adenine's pairing is replaced with </u><u>Uracil</u>while Guanine/Cytosine pairing remains the same.
hence, the main difference between the base-pairing during both processes is the replacement of Thymine with Uracil during transcription.