1. Population genetics and speciation
Chapter 16
Population genetics and speciation

2. Section 1 Genetic Equilibrium
Population genetics-is the study of evolution from a genetic point of view.
Evolution at the genetic level is called microevolution
a change in the genetic material of a population
Genetic material of organisms consists of many alleles-or variations-of many genes that code for various traits
Do you remember that a population consists of a group of individuals of the same species that routinely interbreed?
Populations are the smallest unit in which evolution occurs

3. Causes of Variation What causes variation in traits? Environment
Heredity
Some occur as a range of phenotypes
Range of body sizes
Two colors of flowers
What causes genes to vary?
Mutation- random change in genes that is passed on
Recombination-reshuffling of genes in a diploid offspring
Random pairing-organisms produce large quantities of gametes. This ensures the union of gametes is partly a matter of chance.

4. The Gene pool
Population genetics uses the term gene pool to describe the total genetic information available in a population

5. Hardy-Weinberg Genetic Equilibrium
Unless acted on by an outside influence, genotype frequencies will stay the same.
If the next 5 items occur, there will be no genetic variation
No net mutations occur; alleles remain the same
Individuals neither enter or leave the population
The population is large; infinitely large
Individuals mater randomly
Selection does not occur

6. Section 2 Disruption of genetic equilibrium
Remember—Evolution is a change in a populations genetic material over generations!!
MUTATIONS
The first requirement for genetic equilibrium is that allele frequencies don’t change due to mutations
Spontaneous mutations occur constantly, but at very low rates
This is at normal conditions
When mutagens are introduced, this will affect genetic equilibrium, by producing totally new alleles for a new trait
Mutagens increase the rates of mutations
Slow changes in alleles take long periods of time to remove harmful mutations
In the long run, beneficial mutations with arise and be beneficial to evolution

7. Not these mutants

8. Gene Flow
Second requirement for genetic equilibrium, is that the size of the population remains constant.
Immigration- the movement of individuals into a population
Emigration- the movement of individuals out of a population
The constant movement of genes rom one population to another
Gene flow
Gene flow can occur through various mechanisms, such as migration of individuals, or dispersal of seeds or spores

9. Genetic Drift
Third requirement of genetic equilibrium is the presence of a large population
The Hardy-Weinberg principle is based on probability
Genetic drift- in the phenomenon by which allele frequencies in a population change as a result of random events.
this requires a small to medium sized population

10. Non random Mating
The fourth requirement of genetic equilibrium is random matings, without care of genetic makeup.
Many species do not mate randomly
Mating influenced by geographic
Many species chose mates with similar traits
The selection of a mate based on similar traits is called assortative mating
Nonrandom mating affects what alleles will be combined within individuals, but does not affect the overall frequencies within a population

11. Sexual Selection
The tendency to choose a mate based on certain traits

12. Natural Selection
The fifth and final requirement of genetic equilibrium is the absence of natural selection.
Natural selction is ongoing, and therefore disrupts genetic equilibrium.
Remember!!! Natural selection means some members of a population are more likely than others to survive and reproduce, passing their genes to the next generation.
Remember that natural selection works off 4 different variables
When natural selection is working, the distribution of traits shift between 3 types of bell curves
Stabilizing selection
Disruptive selection
Directional selection

13. Stabilizing Selection
Individuals with the average form of a trait have the highest fitness

14. Disruptive selection
Individuals with either extreme variation of a trait have greater fitness that individuals with the average form of a trait

15. Directional selection
Individuals that display a more extreme form of a trait have greater fitness than individuals with an average form of the trait.