1. Genes and Variations

2. Genetics and Evolutionary Theory
In genetics terms, evolution involves a change in the frequency of alleles in a population over time.
Natural selection occurs through the phenotype, not the genotype.
Remember that phenotypes include all visible characteristics physiological characteristics, like height or eye color.

3. Populations and gene pools
A gene pool includes all genes, including alleles for each gene, within a given population.
Allele frequency- the rate in which a gene occurs in a gene pool.
IMPORTANT- remember that populations, not individuals, evolve.

4. Sources of variation
There are three major sources of genetic variation within a population:
1. mutation
2. genetic recombination
3. lateral gene transfer

5. Mutation Mutation is any change within the genetic material of a cell.
Some mutations do not affect fitness, some lower it, and some raise fitness.

6. Mutation is more common than we think.
There are approximately 300 gene mutations in our DNA that make us different from our parents.
Mutation is only important in evolution if the trait can be passed on.

7. Genetic recombination in sexual reproduction
Crossing over is another way genes are combined.
In this process, genetic material is physically exchanged by paired chromosomes mostly during the formation of sperm and egg cells (meiosis).
This is another reason why
members of the same species can
differ from one another.

8. Lateral gene transfers
Lateral gene transfer occurs between organisms by the direct swapping of DNA.
Bacteria can trade bits of DNA called plasmids amongst themselves and other populations.
The passing of genetic material on to another organism that is not it’s offspring is called lateral gene transfer.
Think back to Griffith’s experiment…

9. Single Trait Genes
The number of phenotypic effects that can occur within a population depends on how many genes affect a single trait.
Single trait genes mean:
one gene= one trait.
For example: six finger gene (polydactyl). You can either have the six finger dominant allele, or the five finger recessive allele.

10. Polydactyl not polydactyl

11. Polygenic traits
Polygenic traits are traits that are controlled by many genes.
(poly=many) (genic= gene)
Example hair color: You could be bright blonde, honey blonde, dirty blonde, strawberry blonde, brown, light brown, dark brown, auburn…etc…

13. Natural Selection on Single Gene traits
Natural selection of a single trait can lead to a change in allele frequency, and thus change phenotypic frequencies.

14. The Effects of color mutation on Lizard Survival

15. Natural Selection on Polygenic Traits
When traits are controlled by many genes, natural selection becomes more complex. This complexity can be represented using a bell curve (graph).

16. This produces one of three types of natural selection:
Natural selection on polygenic traits can affect the relative fitness of phenotypes.
This produces one of three types of natural selection:
Directional
Stabilizing
Disruptive

17. Directional selection
Individuals at one end of the curve have a higher fitness than the others.
Example: In an area with thick seeds, birds with larger beaks are able to feed more easily. This in turn will show over time the average size beak of birds in that area will increase.

19. Stabilizing
Individuals in the middle of the curve have higher fitness.
Example: Mass size in human babies. Babies of average mass are more likely to survive than those that are too heavy or too thin.

21. Disruptive
When individuals in the extremities of the curve have a higher fitness than the middle of the curve. In this case, if the selective pressure is left long enough, then the curve may separate into two new curves.
Example: In a bird population where medium beaks are less common, the birds with drastically larger or smaller beaks may be more fit.

23. Genetic Drift
In a population individuals may pass a certain allele on to their offspring more by random chance.
Over time the frequency of an allele becomes less common.

24. Genetic Drift: Bottleneck effect
A change in an allele frequency that dramatically changes a population. Often occurs in a severe selective pressure, like a disease.

25. Genetic Drift: Founder Effect
When a small population breaks off of another larger population by means of migration or separation; this is called the founder effect.

26. Evolution Vs. Genetic equilibrium
If an allele pool in a population is not changing, they are not evolving and are at genetic equilibrium.

27. Sexual Reproduction and Allele Frequency
Remember that chromosomes have no set way that align in an meiotic cell so…
If there is not a change in allele frequency within the population, there will be no shift in population frequency. This can lead to a population being in genetic equilibrium.