Question

Which of these four gene parts should allow the construction of the most accurate phylogenetic tree, assuming that this is the only part of the gene that has acted as a reliable molecular clock?]?

Answer 1

I believe the answer is Intron IV, Introns are non-coding regions while exons are the coding regions. In most eukaryotic genes, coding regions (exons) are interrupted by non coding regions (introns). During transcription, the entire gene is copied into a pre-mRNA splicing, introns are removed and exons joined to form a contiguous coding sequence.