1. Chapter 16

2. Population genetics
Population: a localized group of individuals belonging to the same species
Species: a group of populations whose individuals have the potential to interbreed and produce fertile offspring
Gene pool: the total aggregate of genes in a population at any one time
Population genetics: the study of genetic changes in populations
Modern synthesis/neo-Darwinism
“Individuals are selected, but populations evolve.”

3. Hardy-Weinberg Theorem
Serves as a model for the genetic structure of a nonevolving population (equilibrium)
5 conditions:
1- Very large population size;
2- No migration;
3- No net mutations;
4- Random mating;
5- No natural selection

4. Hardy-Weinberg Equation
p=frequency of one allele (A); q=frequency of the other allele (a); p + q= (p=1-q & q=1-p)
P2=frequency of AA genotype; 2pq=frequency of Aa plus aA genotype; q2=frequency of aa genotype; p2 + 2pq + q2 = 1.0

5. Microevolution, I New definition of Evolution at the population level.
Evolution is a generation to generation change in a population’ s frequencies of alleles.
This also can be called microevolution: A change in the gene pool of a population over a succession of generations
1- Genetic drift: changes in the gene pool of a small population due to chance (usually reduces genetic variability)

6. Figure Genetic drift

7. Microevolution, II
The Bottleneck Effect: type of genetic drift resulting from a reduction in population (natural disaster) such that the surviving population is no longer genetically representative of the original population

8. Microevolution, III
Founder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population

9. Microevolution, IV
2- Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

10. Microevolution, V
3- Mutations: a change in an organism’s DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)
4- Nonrandom mating: inbreeding and assortive mating (both shift frequencies of different genotypes)
5- Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment

11. Population variation
Polymorphism: coexistence of 2 or more distinct forms of individuals (morphs) within the same population
Geographical variation: differences in genetic structure between populations (cline)

12. Figure 23.8 Clinal variation in a plant

13. Two Random Processes that generate genetic variation
Mutation – new alleles originate only by mutation. Rare and random events and usually occur in somatic cells and are not passed on to the offspring.
Sexual Recombination combines old alleles with new and fresh assortments every generation.

14. Variation preservation
Prevention of natural selection’s reduction of variation
Diploidy 2nd set of chromosomes hides variation in the heterozygote
Balanced polymorphism 1- heterozygote advantage (hybrid vigor; i.e., malaria/sickle-cell anemia); frequency dependent selection (survival & reproduction of any 1 morph declines if it becomes too common; i.e., parasite/host)

15. Natural selection
Fitness: contribution an individual makes to the gene pool of the next generation
3 types:
A. Directional
B. Diversifying
C. Stabilizing

16. Figure 23.12 Modes of selection

17. Sexual selection
Sexual dimorphism: secondary sex characteristic distinction
Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism

18. 16.3 Maintenance of Diversity
Biology, 9th ed,Sylvia Mader
Chapter 18
16.3 Maintenance of Diversity
Genetic Variability
Populations with limited variation may not be able to adapt to new conditions
Maintenance of variability is advantageous to the population
Only exposed alleles are subject to natural selection 18
Processes of Evolution

19. Maintenance of Diversity
Biology, 9th ed,Sylvia Mader
Chapter 18
Maintenance of Diversity
Natural selection causes imperfect adaptations
Depends on evolutionary history
Imperfections are common because of necessary compromises
The environment plays a role in maintaining diversity
Disruptive selection due to environmental differences promotes polymorphisms in a population
If a population occupies a wide range, it may have several subpopulations designated as subspecies
The environment includes selecting agents that help maintain diversity 19
Processes of Evolution

20. Maintenance of Diversity
Biology, 9th ed,Sylvia Mader
Chapter 18
Maintenance of Diversity
Recessive alleles:
Heterozygotes shelter recessive alleles from selection
Heterozygotes allow even lethal alleles to remain in the population at low frequencies virtually forever
Sometimes recessive alleles confer an advantage to heterozygotes
The sickle-cell anemia allele is detrimental in homozygote
However, heterozygotes are more likely to survive malaria
The sickle-cell allele occurs at a higher frequency in malaria prone areas 20
Processes of Evolution

21. Maintenance of Diversity
Biology, 9th ed,Sylvia Mader
Chapter 18
Maintenance of Diversity
Heterozygote Advantage
Assists the maintenance of genetic, and therefore phenotypic, variations in future generations.
In sickle cell disease heterozygous individuals don’t die from sickle-cell disease, and they don’t die from malaria. 21
Processes of Evolution