240 ❯ STEP 4. Review the Knowledge You Need to Score High
- Why does heterozygote advantage protect recessive genes from being eliminated?Those who
are heterozygous for the condition are receiving some benefit. For example, those who
have sickle trait are protected against malaria. This positive benefit for heterozygous
individuals helps keep the recessive condition alive in the population.
Key Skills- Use data from a changing population and analyze it using the Hardy-Weinberg equation.
- Explain how data from using this equation demonstrates genetic drift and the effects of
selection.
Investigation 3: Comparing DNA Sequences to Understand
Evolutionary Relationships with BLAST
Say you found a brand-new fossilized creature buried in your backyard, and you want to
find its closest living relative. Or maybe you identified a single gene that causes disease in
hedgehogs and you want to know if that same gene is found in humans. This lab focuses
on the use of BLAST (Basic Local Alignment Search Tool) as a tool to answer such ques-
tions. In addition, it incorporates the use of cladograms. A cladogram is a visual represen-
tation of the evolutionary relatedness of a species. In this investigation, you will use BLAST
to generate the information needed to construct a cladogram.Basic Setup
Given a genetic sequence, you are required to use the online BLAST software to compare
it to other gene sequences already in their gigantic database. Results will show a ranking of
the most closely related organisms (and what percentage of their base pairs actually match up).
Just as in the previous lab, you won’t have a computer available to you during the AP exam,
so no, you won’t have to actually know how to use BLAST while taking the test. You will,
however, most likely need to analyze data obtained from a hypothetical BLAST query and,
from those results, generate a cladogram depicting evolutionary relatedness.Results
By determining the percent similarity of an unknown gene with those from other organ-
isms, you should be able to then place your unknown creature within a cladogram to show
evolutionary relatedness. For example, say you had a table showing the percent similarity
of “gene X” in humans versus four other species (see Table 19.1).
If you drew a cladogram showing the evolutionary relationship, it would look some-
thing like Figure 19.1.Table 19.1 Percent similarity between gene X in humans and other species.
SPECIES GENE PERCENT SIMILARITY COMPARED TO HUMANS
A 98%
B 91%
C 70%
D 52%BIG IDEA 1
Evolution