Download HW20PolygenicEvo2014

Biology Homework 20 (2014)
Polygenic Evolution and Selection
Part 1: Background (Take quick notes in your journal)
Biological evolution is defined as a change in gene frequency over time. We can measure this change for
simple dominant and recessive traits using the Hardy-Weinberg equilibrium. However, most traits are
not based on simple dominant and recessive relationships—most are dependent upon more than one
gene or POLYGENIC.
Part 2: Graph 1
We measure change in gene frequencies of polygenic traits by first sampling a population and measuring
a particular trait. In the following example, please graph the following data for two moth populations.
Population 1 was studied in Deming, WA and population 2 was sampled in Seattle, WA. The color 1
represents a white moth, while a color 9 represents a black moth and the colors in between numbers
represents shades of grey.
A. Copy and complete the data table in your journal.
B. Create a line graph of the data in your journal.
Number of Moths of each color
Color
1
2
3
4
5
6
7
8
9
Total
Population 1-Deming
6/1/93 Color x # 6/1/13
3
0
7
4
10
5
18
10
24
19
18
26
10
24
7
9
3
3
100
100
Color x #
Color
1
2
3
4
5
6
7
8
9
Total
Population 2-Seattle
6/2/93 Color x # 6/2/13
1
3
6
10
12
20
18
23
24
18
18
14
13
6
7
4
1
2
100
100
Color x #
C. Write out and answer the following questions
a. What was the change in mean gene frequency for population 1? (Show your
calculations for mean gene frequency) How do you know this?
b. What was the change in mean gene frequency for population 2? (Show your
calculations for mean gene frequency) How do you know this?
c. Are the populations diverging? Explain.
d. Explain a possible cause for the changes seen in both populations—be specific.
More on the back 
Part 3: Background (Take quick notes in your journal)
Selective pressure can affect the distribution of traits (phenotypes) in any of three ways: Directional
Selection, Stabilizing Selection and Disruptive Selection. In directional selection, the entire curve moves
either to the right or to the left. This type of evolution causes the number of individuals with a
particular trait to increase at one end of the curve. In Stabilizing Selection, the center of the curve (the
central tendency) remains the same, but the relative number of individuals at the center increases due
to increased fitness. In this type of selection, the curve gets taller. In Disruptive Selection, the
individuals at either end of the curve increase in relative numbers and the number at the center
decreases. This creates a graph that looks like two humps on a camel’s back and is called a bimodal
distribution.
In your journals, using the information above, make 3 rough graphs of each type of evolution. Label the
type for each and the x and y axis. You are welcome to use whatever organism and phenotype you like.
Part 4: Graph 2
A. Copy and complete the table in your journal.
B. Create a line graph of the following data.
Population 1-Deming
Finch Beak Size 7/4/98
7/5/08
4.8 mm
0
1
4.9 mm
0
4
5.0 mm
3
9
5.1 mm
7
17
5.2 mm
10
21
5.3 mm
18
10
5.4 mm
24
3
5.5 mm
18
7
5.6 mm
10
18
5.7 mm
7
13
5.8 mm
3
5
5.9 mm
1
3
6.0 mm
0
1
Total
C. Write out and answer the following questions
a.
b.
c.
d.
e.
Calculate the total population for both years.
What is the mode of the finch beak length at 7/4/98?
What is(are) the mode(s) of the finch beak length at 7/5/08?
What kind of selection is this?
What could cause this type of evolution with these finches? Be specific.
More on the back 