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Period
SECTION
11.2
NATURAL SELECTION IN POPULATIONS
Study Guide
KEY CONCEPT
Populations, not individuals, evolve.
VOCABULARY
normal distribution
stabilizing selection
microevolution
disruptive selection
directional selection
MAIN IDEA: Natural
selection acts on a distribution of traits.
1. What is a phenotypic distribution?
graph that shows the frequency of each phenotype for a trait in a population
2. What can you learn from looking
at a phenotypic distribution?
how common each phenotype is in the population; whether or not the
population is undergoing natural selection for the trait
3. In a population
that is not undergoing natural selection for a certain trait, u/hat does the
phenotypic distribution look like?
a normal distribution or a bell-shaped curve
In the space provided below, draw the phenotypic distribution for a trait that follows
distribution. Be sure to label the axes as well as the mean phenotype.
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a normal
Graph should resemble a bell-shaped curve.
X-axis should be labeled "range" or "range of phenotypes"
Y-axis should be labeled "frequency".
Mean phenotype should be labeled in the center of the curve, which is
also the peak of the curve.
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Unit 4 Resource Book
McDougal Littell Biology
Srudy
Guide 35
Namc
Period
Date
STUDY GUIDE, CONTINUED
MAIN IDEA: Natural
selection can change the distribution of a
trait in one of three
\üays.
In the table below, take notes about the three patterns ofnatural selection.
Type of Selection
4.
directional
selection
5.
stabilizing
selection
6.
disruptive
selection
How lt Works
Graph
Favors phenotypes at one
extreme of a trait's range
graph should show a
normal distribution
shifted either to the
right or left.
Favors intermediate
phenotypes/selects against
phenotypes at both extremes
graph should show
distribution with
sharp peak in the
center at the mean.
Favors phenotypes at both
extremes of a trait's range/
selects against intermediate
phenotypes
graph should show
distribution with one
peak at each extreme.
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Vocabulary Gheck
:
9. During disruptive
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7. The observable change in allele frequencies over time is called microevolution.
8. During stabilizing
selection, the intermediate phenotype is selected for.
study Guide
directional
selection, both extreme phenotypes are selected for.
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selection, the mean phenotype changes.
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Unit 4 Resource Book
McDougal Littell Biology