1. Chapter 15: Evolution of Populations
Biology 1

2. Variation Inherited differences between individuals of a population
Can be
Physical characteristic
Biochemical characteristic
Behavioral characteristic
If there is no variation for a
trait, it is said to be fixed

3. Gene Pool All of genes found within a population
Relative frequency of alleles- proportion of gene pool that the allele makes up

4. Sources of Variation Mutation Gene Shuffling
Creates new variation by changing parts of the genetic code
Gene Shuffling
Creates new variation by the reshuffling of genes during sexual reproduction
Chromosome segregation
Crossing-over

5. Single Gene Traits Traits are coded for by a single gene
If trait has simple Mendelian (dominant/recessive) inheritance, there are 2 phenotypes possible.
If trait has incomplete dominance or codominance, there are 3 phenotypes possible.
If trait has multiple alleles, # of phenotypes depends on # of alleles
For example: ABO blood type have 3 alleles with 4 phenotypes possible

6. Natural Selection on Single Trait Genes
Occurs if the phenotypes are not equal in their fitness
Relative frequencies within the gene pool change as some phenotypes are selected for (or some are selected against)
This is evolution (a change in allele frequencies within a population over time)
Natural Selection Refresher

7. Polygenic Traits Trait is coded for by more than one gene
Various phenotypes possible
Phenotypes form a bell curve

8. Natural Selection of Polygenic Traits
Directional Selection
One phenotype extreme is selected for (or one against)
Bell curve is shifted to the left or right

9. Natural Selection of Polygenic Traits (continued)
Stabilizing Selection
Both phenotype extremes are selected against (average phenotype is selected for)
Bell curve narrows

10. Natural Selection of Polygenic Traits (continued)
Disruptive Selection
Average phenotype is selected against (extremes are selected for)
Bell curve splits into two peaks

11. Genetic Drift Change in allelic frequencies due to random effects
Effects are seen more in smaller populations

12. Genetic Drift: Bottleneck Effect
Event randomly removes large numbers of individuals from a population
Many variations can be lost

13. Genetic Drift: Founder Effect
Small part of the population removes itself (or is removed) from the larger population

14. Genetic Equilibrium Allelic Frequencies remain the same No evolution
Random mating
Large population
No immigration or emigration
No mutation
No natural selection

15. Speciation
Species - group of individuals that can breed together and produce a fertile offspring
Speciation is the process of forming new species from existing species
To occur:
Populations of one species must be isolated from each other long enough to accumulate enough changes to become two species

16. Types of Isolation Geographical Isolation
Populations are separated by a geographical barrier and cannot mate and share genes

17. Types of Isolation Behavioral Isolation Temporal Isolation
Populations are separated by behavioral differences and don’t mate with each other to share genes
Temporal Isolation
Populations reproduce at different times so they cannot mate together and share genes

18. This leads to… Reproductive Isolation
Cannot mate and produce a fertile offspring
Occurs because individuals cannot
Mate together or
Create a zygote
Create a viable offspring
Create a fertile offspring

19. EVOLUTIONARY TRENDS Adaptive Radiation from COMMON DESCENT
Species diversifies into many new species

20. EVOLUTIONARY TRENDS Convergent Evolution-Analogous Structure
Species evolve to a similar form from different ancestors
Both adapt to similar environment
Examples

21. EVOLUTIONARY TRENDS Coevolution
Species evolve together because of a close ecological relationship
Coevolution Examples

22. EVOLUTIONARY TRENDS Punctuated Equilibrium
Evolution shows long stable period and then rapid bursts of change