Final answer:
A chemical mutagen altering the 5' end of an intron may result in the inclusion of that intron in the mRNA, potentially leading to a dysfunctional protein.
Step-by-step explanation:
If exposure to a chemical mutagen results in a change in the sequence that alters the 5' end of intron 1 (I1) in a eukaryotic transcript, the most likely outcome could be the inclusion of I1 in the mRNA. Introns are typically removed from the pre-mRNA during splicing to form mature mRNA. However, mutations at the splice sites, such as the 5' end of the intron, may interfere with the splicing machinery's ability to recognize and properly remove the intron. The inclusion of intron sequences in the mRNA can lead to the synthesis of a dysfunctional or nonfunctional protein due to the presence of extra, unintended sequences within the coding region.