1. Chapter 18: Evolutionary Change in Populations

2. Remember: Basis of evolution is GENETIC
We study POPULATIONS (not in an individual lifetime)
Variations are due to
ENVIRONMENT
HEREDITY

3. Populations genetics
Study of genetic variability within a population and of the forces that act on it

4. 5 factors responsible for evolutionary change:
Nonrandom mating
Mutation
Genetic drift
Gene flow
Natural selection

5. Gene pool All the alleles for all genes present in the population
Genotype frequency
Phenotype frequency
Allele frequency

6. Hardy-Weinberg
Genetic equilibrium – allele and genotypes frequencies do not change between generations
Ideal situation – rare
Provides model
Equation:

8. The occurrence of PKU is 1 per 10,000 births
q2 =
q = 0.01
The frequency of normal alleles is
p = 1 – q = 1 – 0.01 = 0.99
The frequency of carriers is
2pq = 2 x 0.99 x 0.01 =
or approximately 2% of the U.S. population

9. Conditions for Hardy-Weinberg
1.) Random Matings
2.) No net mutations
3.) Large population size
4. ) No migration
5.) No natural selection

10. Hardy-Weinberg Problems
Page 405 of textbook
Review Questions
(# 1-10)
Check answers in Appendix
Bring questions to class

11. Microevolution
Generation-to-generation changes in allele or genotype frequencies within a population
5 processes at work:
Nonrandom mating
Inbreeding
Assortative breeding
Mutation
Genetic drift
Bottleneck effect
Founder effect
Gene flow
Natural selection

12. Generation 1 Generation 2 Generation 3 p (frequency of CR) = 0.7
Fig
CR CR
CR CR
CW CW
CR CR
CR CR
CR CW
CR CW
CR CR
CR CR
CW CW
CR CR
CR CR
CW CW
CR CR
CR CR
CR CW
CR CW
CR CR
CR CR
CR CR
CR CR
CR CW
CW CW
CR CR
Figure 23.8 Genetic drift
CR CR
CR CR
CR CR
CR CW
CR CW
CR CW
Generation 1
Generation 2
Generation 3
p (frequency of CR) = 0.7
p = 0.5
p = 1.0
q (frequency of CW ) = 0.3
q = 0.5
q = 0.0

13. Original population Bottlenecking event Surviving population
Fig. 23-9
Figure 23.9 The bottleneck effect
Original
population
Bottlenecking
event
Surviving
population

14. Fig
Figure Gene flow and human evolution

15. Natural Selection – 3 types
Stabilizing selection – intermediate phenotypes
Directional selection – 1 extreme phenotype
Disruptive selection – favors phenotypic extremes

16. Frequency of individuals
Fig
Original population
Frequency of individuals
Phenotypes (fur color)
Original
population
Evolved
population
Figure Modes of selection
(a) Directional selection
(b) Disruptive selection
(c) Stabilizing selection

17. Genetic Variation is Necessary for Natural Selection
Sources of Variation
Mutation
Sexual reproduction
Meiosis
Crossing over
Independent assortment
Random union of gametes

18. Genetic Polymorphism
Presence in a population of 2+ alleles for a give locus
Variation
Low frequency of alleles

19. Balanced polymorphism
Type of genetic polymorphism
2+ alleles persist in a population over many generations because of natural selection
2 types:
Heterozygote advantage
Sickle cell
Frequency-dependent selection
More value when rare

20. Plasmodium falciparum (a parasitic unicellular eukaryote) 7.5–10.0%
Fig
Frequencies of the
sickle-cell allele
0–2.5%
Figure Mapping malaria and the sickle-cell allele
2.5–5.0%
5.0–7.5%
Distribution of
malaria caused by
Plasmodium falciparum
(a parasitic unicellular eukaryote)
7.5–10.0%
10.0–12.5%
>12.5%

21. “left-mouthed” individuals
Fig
“Right-mouthed”
1.0
“Left-mouthed”
“left-mouthed” individuals
Frequency of
0.5
Figure Frequency-dependent selection in scale-eating fish (Perissodus microlepis)
1981
’82
’83
’84
’85
’86
’87
’88
’89
’90
Sample year

22. Neutral Variation
Variation that does not alter the ability of an individual to survive and reproduce so is not adaptive