Evolution PCB4674
Hardy-Weinberg equilibrium practice questions
1
You observe a field of wildflowers with the following genotype frequencies: AA:
44, Aa: 66, aa: 22. What are the allele frequencies? Is this population in HardyWeinberg equilibrium?
obs genotype
genotyp freq allele freq
exp genotype
exp #s
AA
44
0.33333333
0.58333333
0.340277778
44.9166667
Aa
66
0.5
0.486111111
64.1666667
aa
22
0.16666667
0.41666667
0.173611111
22.9166667
132
Yes
2
Given initial allele frequencies of A: 0.3 and a: 0.7, calculate the final allele
frequencies for a population of 10000 individuals one generation later assuming HW
conditions are met. What are the genotype frequencies?
A: 0.3 a:0.7
allele freq
exp genotype
AA
0.3
0.09
Aa
0.42
aa
0.7
0.49
3
Repeat question 2 assuming that mutation converts A to a at a rate of 1 in 10000.
allele freq exp genotype exp #s allele freq mutation
allele freq
AA
0.3
0.09 900
0.3 0.3+(0.0001x0.3)
0.29997
Aa
0.42 4200
aa
0.7
0.49 4900
0.7 0.7+(0.0001x0.3)
0.70003
4
Given initial allele frequencies of A: 0.3 and a: 0.7, calculate the final allele
frequencies and genotype frequencies for a population of 10000 individuals one
generation later if selection eliminates 20% of the heterozygotes.
exp genotype exp #s selection
exp #s
allele freq
allele freq
AA
0.09 900
900+1680
2580/9160
0.28
Aa
0.42 4200 -840=3360
aa
0.49 4900
4900+1680
6580/9160
0.72
5
Repeat question 4 assuming that selection eliminates 20% of the individuals with
allele A regardless of whether they are homozygous or heterozygous.
exp genotype exp #s selection
exp #s
allele freq
allele freq
AA
0.09 900
-180=720 720+1680
2400/8980
0.27
Aa
0.42 4200 -840=3360
aa
0.49 4900
4900+1680
6580/8980
0.73
6
Starting with initial allele frequencies of A: 0.5 and a: 0.5, and a population of
9000 viable zygotes, calculate the final allele frequencies if the population receives an
influx of 1000 individuals with genotypes AA: 100, Aa: 800, aa: 100. Has the migration
caused the population to evolve?
exp genotype exp #s migration
exp #s
allele freq
allele freq
AA
0.25 2250 +100=2350 2350+2650
5000/10000
0.5
Aa
0.5 4500 +800=5300
aa
0.25 2250 +100+2350 2340+2650
5000/10000
0.5
7
Starting with the following number of individuals in each genotype AA: 1000,
Aa: 1000, aa: 1000, convince yourself that selfing decreases heterozygotes and increases
homozygotes by following the population through 3 generations.
0
1
2
3
AA
1000
1250
1375
1437.5
+250
+125
+62.5
Aa
1000
500
250
125
+250
+125
+62.5
aa
1000
1250
1375
1437.5