Certified Histocompatibility Specialist Practice Test

The correct answer is based on the principle of how reading frames work in nucleic acid sequences. In any given segment of DNA, particularly within a coding region, there are multiple ways to interpret the sequence in terms of potential protein-coding sequences, which is what reading frames represent. For a eukaryotic DNA sequence, the coding region (exon) is read in triplets called codons, and since DNA is double-stranded, each strand can serve as a template for translation. In a single-stranded context, the sequence can be read in three possible frames starting from one of the three nucleotides. Additionally, because a DNA sequence is bi-directional (it can be read from both strands), you can also derive three reading frames from the complementary strand. This results in a total of six reading frames: three from the original strand and three from the reverse complementary strand. In this scenario, you have a 200bp DNA sequence containing an exon of 180bp. While the length of the exon is significant, it does not change the calculation of how many reading frames are created from the entire sequence. Thus, the total possible reading frames for this exon-containing sequence is six, confirming that the understanding of reading frames in