EXERCISE QUESTIONS
13.1 Hardy-Weinberg Law (LM pages 164–67)
Observation: The Baseline (LM pages 165–66)
1.
Taste a piece of paper impregnated with PTC. Can you taste this chemical? The
answer will depend on the individuals tasting the paper. What is your genotype? Persons who
can taste the chemical are either TT or Tt. Persons who cannot are tt.
2.
Do you have attached or unattached earlobes? The answer will depend on the
particular student. What is your genotype? Those who have unattached earlobes are either EE
or Ee. Those who do not are ee.
3.
Determination of homozygous recessive frequency (q2):
a.
What percentage of the population (class) is unable to taste PTC? Answer will
depend on class data.
b.
What percentage of the population (class) has attached earlobes? Answer will
depend class data.
6.
b.
Why is this reasonable, considering that you are dealing with one allelic pair
of genes? The number 1 represents 100%. Since we are dealing with only two genes, the two
frequencies together must add up to 100%.
Table 13.1 Determination of q2, q, p, p2 and 2pq*
Trait
q2
q
p
PTC tasting
0.25
0.5
0.5
Earlobes
0.16
0.4
0.6
p2
0.25
0.36
2pq
0.50
0.48
*Actual results will depend on class, but the data in this table are based on an assumption of a
total of thirty-two students in the class.
9.
Then calculate the number of students who are homozygous dominant:
Homozygous dominant frequency (p2) x total number of students = Answer will depend on
class data.
Calculate the number of students who are heterozygous: Heterozygous frequency (2pq) x
total number of students = Answer will depend on class data.
Testing the Hardy-Weinberg Law (LM pages 166–67)
Given your data in Table 13.1, what should the genotypic frequencies be in the next
generation, according to the Hardy-Weinberg law? The frequencies should be the same as
those shown in Table 13.1.
Experimental Procedure: Testing the Law (LM pages 166–67)
2.
Write down your initial parental (P) generation genotype. Answer will depend on
individual results.
Table 13.3 F1 Generation
Answers will depend on results obtained by each couple.
7.
Now fill in Table 13.4, using the F5 information for all members of the population.
To fill in the “Number of Students” column of this table, simply add up the number of students
who report each genotype. For example, assume that ten report the homozygous recessive, six
report the homozygous dominant, and sixteen report the heterozygous. To fill in the “Genotypic
Frequencies” column, simply calculate the percentage of the class for each genotype. For
example, 10/32 = 0.3125 = 0.31 after rounding off. Notice that the total of the percentages
(frequencies) is 1.
Table 13.4 F5 Generation*
Genotypes
Number of Students
Homozygous recessive (q2)
10
2
Homozygous dominant (p )
6
Heterozygous (2pq)
16
*Actual results will depend on class data.
Genotypic
Frequencies
0.31
0.19
0.50
8.
Compare Table 13.4 with Table 13.2. Ideally the two tables will be the same. Do your
results show that your population is in a Hardy-Weinberg equilibrium? yes If not, which of
the conditions listed in the “Introduction” may have been fulfilled? nonrandon mating or
genetic drift
13.2 Genetic Drift (LM pages 167–69)
Experimental Procedure: Founder Effect (LM page 169)
1.
How many persons are in the new population? Example: 16
2.
Complete Table 13.5. Students complete Table 13.5 as they did Table 13.2.
4.
After five generations, fill in Table 13.6. Students complete Table 13.6 as they did
Table 13.4.
5.
Compare Table 13.6 to Table 13.5. Do the results suggest that the size of the
population affects genetic equilibrium and that genetic drift has occurred? yes Explain.
Genetic drift occurs because the “founders” represent only a fraction of the total genetic
diversity of the original gene pool. Also, a small population is subject to genetic drift more than
a large population.