Examine the schematic of a gene shown below. The transcriptional start site (TSS) and trans/ational start (ATG) and stop (TAG) codons are labelled. Exons are indicated by the darker gray boxes, while introns are indicated by the thinner gray boxes. The locations of four variants are indicated by the letters A-D. A variant at location is most likely to lead to a change in protein sequence, while a variant at location most likely to affect transcription levels of the gene. A; D C) A C. B D; A.