CHAPTER 14 GENE EXPRESSION: FROM GENE TO PROTEIN
Scientific Skills Exercise
Teaching objective: Students will compare DNA sequences to identify conserved sequences and
then relate these sequences to their function. The data are presented in a graphical form called a
sequence logo, a way to visually compare sequences that is particularly information-rich.
Teaching tips: The consensus sequence determination should not be difficult for students. The
Many students will recognize the similarity between sequence logos and Web 2.0 tag or data
instead of being randomly arranged in the cloud display, their position along the horizontal and
vertical axes conveys important information regarding sequence and relative frequency. It will be
impossible to distinguish the individual bases in the shortest sequence logo stacks; at best they
can discern the color of the top base to figure out the consensus sequence.
Answers:
1. (a) In the 10 sequences in the sequence alignment at position -9, there are 7 Gs, 2 As, and 1 C,
matching their relative size and placement in the sequence logo G is larger and on top, A is
4. (a) To write a consensus sequence, you would read off the base at the top of each stack at each
position, putting a dash where the base is too small to read. The consensus sequence for this
Suggested Answers for End-of-Chapter Essay Questions
See the general information on grading short-answer essays and the suggested rubric at the
beginning of this document.
10. Scientific Inquiry
The -globin gene contains introns, which could not be spliced out by the bacterial cell. The
11. Focus on Evolution
Given the essential nature of a triplet genetic code, we can assume that each of the 20 amino
acids was originally coded for by one unique triplet codon. Most amino acids are coded for by a
12. Focus on Information
Sample key points:
The fidelity with which DNA is copied and inherited guarantees the continuation of a
species.
Sample top-scoring answer:
DNA, containing the genetic information, is passed along from cell to cell and from generation
to generation. On one hand, the fidelity with which DNA is inherited guarantees the continuation
of each species, and many systems in the cell ensure that the DNA is copied accurately and that
13. Synthesize Your Knowledge
-sensitive mutation in a gene that codes for an
enzyme in the melanin pathway, such as tyrosinase. At the higher temperatures of the central part
-colored