If a cell transcribed and translated a gene's intron by mistake, the most likely outcome would be:
Additional amino acids would be inserted into the chain.
This is because introns are non-coding sequences that are normally removed during RNA processing. If an intron is mistakenly included in the mature mRNA and subsequently translated, it can lead to the production of a protein with additional amino acids corresponding to the sequence of the intron, which can disrupt the normal function of the protein.