1. Topics How to track evolution – allele frequencies
Hardy – Weinberg principle – applications
Requirements for genetic equilibrium
Types of natural selection
Population genetic polymorphism

2. Population gene pool - consists of different combinations
Ch Evolutionary change
in populations, pp
Population gene pool - consists of different combinations
of alleles genetic variation -
the raw material for evolution
Frequencies of genotype, phenotype and alleles in a
population help understand evolution
Changes in allele/genotype frequencies over generations in a
population - microevolution (usually over few generations thus
relatively minor changes)

3. Genotypic, phenotypic or allelic frequencies each sum to 1
Ch Evolutionary change
in populations, p
Genotypic, phenotypic or allelic frequencies
each sum to 1
Changes in allele frequencies determine gene pool
composition over generations
If genotypic or allelic frequencies do not change in a
population over time - genetic equilibrium - no evolution
in that locus

4. Allele frequencies change only when influenced by external factors
Ch Evolutionary change
in populations, p
The conventional view - dominant alleles would eventually come to dominate the gene pool, and the recessives disappear
Allele frequencies change only when influenced by external factors
Stability of populations over time is explained by the Hardy-Weinberg Principle

5. Hardy-Weinberg Principle
Ch Evolutionary change
in populations, p
Hardy-Weinberg Principle

6. Hardy-Weinberg Principle
Ch Evolutionary change
in populations, p
Hardy-Weinberg Principle

7. p2 + 2pq + q2 = 1 (sum of genotype frequencies)
Ch Evolutionary change
in populations, pp
p2 + 2pq + q2 = 1 (sum of genotype frequencies)
When frequency of homozygous recessive genotype (q2) is known, we can calculate all the frequencies (genotype, phenotype and allele) using H-W equation
Because, p + q = 1 (sum of allele frequencies)
When genotype frequencies show stability based on H-W equation - genetic equilibrium - population is not evolving for that gene/allele

8. Requirements for Hardy-Weinberg equilibrium
Ch Evolutionary change
in populations, p
Requirements for Hardy-Weinberg equilibrium
No selective mating - random mating
No net mutations - no change in DNA
No genetic drift - large population size
No gene flow - no migration
No natural selection - all phenotypes equally
adaptive
If these conditions are met - Genetic Equilibrium
If not …

9. Selective/nonrandom mating -
Ch Evolutionary change
in populations, p
Selective/nonrandom mating -
1. Mate with neighbors
Inbreeding: Mating with genetically similar individuals (neighbors - self-fertilization is an extreme) - increases homozygosity - causes inbreeding depression (reduced fitness) in some populations

10. 2. Assortative mating: Selection for mating by phenotype
Ch Evolutionary change
in populations, pp. 406.
2. Assortative mating: Selection for mating by
phenotype
Positive - Increases homozygosity
Negative - Decreases homozygosity
Affects the genotype frequency only at loci of genes
that are involved in mate-choice – unlike in inbreeding

11. 1. Changes in base pairs of genes
Ch Evolutionary change
in populations, p
Mutations –
1. Changes in base pairs of genes
2. Gene reposition/rearrangement
3. Change in chromosome structure
Somatic cell vs. reproductive cell
Introns vs Exons
Cause small deviations in allele frequencies

12. Genetic drift – If population is small
Ch Evolutionary change
in populations, pp. 407.
Mutations do not decide direction of (or force)
evolutionary change, and are not dominant
evolutionary forces, but are the source of genetic
variability for natural selection to work on
Genetic drift – If population is small
Random events (chance) in small breeding populations
can cause changes in allelic frequencies decreasing
genetic diversity within population

13. A major evolutionary force in bottlenecks -
Ch Evolutionary change
in populations, pp
A major evolutionary force in bottlenecks -
reduction in population size - due to
predation, disease, physical environmental
changes etc.
Founder effect - a small part of a large
population breaks away and colonizes a new area
- genetic drift is important

14. Gene flow – In Migrations
Ch Evolutionary change
in populations, p. 408.
Gene flow – In Migrations
Migration between populations - allele movement
Usually increases genetic variability in recipient
population
Eventually reduce variation between populations
- tends to counteract effects of natural selection and genetic drift
50 yrs

15. Natural selection - Operates on phenotype
Ch Evolutionary change
in populations, pp. 409.
Natural selection -
Operates on phenotype
Changes allele frequencies toward increased adaptation - adaptive
evolutionary change - therefore different from other four
Many phenotypes are polygenic - variation within character -
normal distribution

16. Categories depending on the fate of mean
Ch Evolutionary change
in populations, pp
Selection
Natural Selection
Ecological Selection
Sexual Selection
Artificial Selection
Group selection - individual fitness depends on group structure or group behavior
Categories depending on the fate of mean

17. Genetic Variation in Population
Ch Evolutionary change
in populations, pp
Genetic Variation in Population
Genetic polymorphism – SNPs and CNVs
Balanced polymorphism – heterozygote advantage and
frequency-dependent may help
long term stability of certain alleles
Neutral variation
Clinal variation