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WLHS / AP BIO / Monson
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PRELAB for AP INVESTIGATION #3: Comparing DNA Sequences to Understand
Evolutionary Relationships with BLAST
**Read through the entire laboratory packet and answer the questions below. This will be stamped for
completion and reviewed before we do the lab!
Introduction:
1) How many genes define a human being?
2) What are two practical uses or applications of having genetic information and DNA sequences readily
available online?
3) What is meant by “bioinformatics”?
4) What is meant by “BLAST”?
5) What is a cladogram / what does it show?
6) Study Figure 1 in the lab packet. Explain the relationships among the 3 species shown in the
cladogram. (i.e. which are most closely related? which is the most distant ancestor?)
7) Study Figure 2. This figure includes derived characters. What are derived characters?
8) According to Figure 2,
a) Which organisms have lungs?
b) What 3 structures do all lizards possess?
c) Which structure evolved first: dry skin or hair?
9) Given that chimpanzees & humans share 95%+ of their DNA, and humans & fruit flies share approx.
60% of their DNA, draw a cladogram depicting the evolutionary relationship among humans,
chimpanzees, fruit flies, and mosses.
Getting Started
1) Use the data in Table 1 to construct a cladogram of the major plant groups.
2) GAPDH (glyceraldehydes 3-phosphate dehydrogenase) is an enzyme that catalyzes the sixth step in
glycolysis , an im portant reaction that paroduces molecules used in cellular respiration. Study the data
for this gene & the protein it expresses shown in Table 2.
a) Why is the percentage similarity in the gene always lower than the percentage similarity in the protein
for each of the species? (HINT: recall how a gene is expressed to produce a protein)
b) Draw a cladogram depicting the evolutionary relationships among all five species (including humans)
according to their percentage similarity in the GAPDH gene.
Sample alignment of
DNA sequences: