1. Evolution of Populations
goal: to understand how populations evolve to form new species

2. Genes and Variation Genotype and Phenotype
Organisms have two set of genes, one from the mother and one from the father. Specific forms of a gene are called alleles.
A person’s genotype is referring to their particular combination of alleles.
A person’s genotype along with the environmental conditions refers to the phenotype (eye color, height, hair color, etc.).
Natural selection acts on the individual’s phenotype not the genotype. Nature will select characteristic not alleles.
Nature will select which phenotype is better suited for the environment and as a result more copies of their genes will be passed on since they have better fitness.

3. Population and Gene Pools
A population refers to a group of individuals that are of the same species and produce offspring.
Members of the same population share a common set of genes and this is known as the gene pool.
The allele frequency refers to the number of times an allele occurs in a gene pool compared to the total number of alleles in that pool for the same gene.
If the allele frequency changes then the population is evolving.
Individuals may evolve but changes in the allele frequency show up in a population.

4. time to think
Question Calculate the total number of alleles? Two – red and white
Question: What is the allele frequency of each allele? Your answer should be in a percentage?
White = 66% Red = 33%

5. Sources of genetic variation
Mutations
Mutations either involve individual genes or larger pieces of chromosomes.
Some mutations are neutral since they don’t change the organisms phenotype
Mutations that matter to evolution occur in germ line cells (sperm and egg) since they can be passed on from generation togeneration.
Mutations that occur in skin cells cannot be passed on to the next generation.

6. Genetic Recombination in Sexual Reproduction
Independent assortment and crossing over during meiosis provide inheritable variation.
These two processes increase the number of genotypes created in each generation.

7. Lateral Gene Transfer
Simple forms of life, like bacteria, can increase genetic variation by simply picking up genes from other organisms through the process called lateral gene transfer.

8. Single-Gene and Polygenic Traits
Single – Gene Traits
The number of phenotypes produced for a certain trait depends on how many genes control the trait.
If a there are two or three distinct phenotypes than a single gene may be responsible and this is known as a single – gene trait.

9. Question: What is the frequency for having the widow’s peak? 75%
A widow’s peak is an example of a single gene trait. There is one gene with two alleles for this trait, one allele for the trait (W) and one for not having the trait (w). If you complete the Punnet Square you can see the frequency of the phenotypes. If you are not familiar with Punnet Squares refer to page 316 of Biology Miller & Levine
Question: What is the frequency for having the widow’s peak?
75%
Question: What is the frequency for not having the widow’s
peak? 25% W w WW Ww ww

10. Polygenetic Traits
When traits are controlled by two or more genes they are considered polygenic traits. Each gene often has two or more alleles.
An example of polygenic traits would be human blood types. This polygenic trait is controlled by three alleles, A, B and O.
Allele Aand B are dominant to allele O which is recessive.
There are fourblood types; A, B, AB and O.

11. 17.2 Evolution as Genetic Change in Populations
How Natural Selection Works
Natural Selection on single–gene traits
Evolution is any change, over time, of the allele frequency in a population.
Natural selection on single-gene traits can lead to changes in allele frequencies and will then lead to changes in phenotype frequencies.
If there is no pressure from natural selection then there will be no change on fitness. If there is selective pressure then there will a change in fitness

12. Does colour affect fitness of lizards?
Why or why not?

13. Natural Selection on Polygenetic Traits
Natural selection polygenic traits in three types of on results selection;
directional selection,
Stabilizing selection
disruptive selection.

14. Directional selection occurs when individuals at one end of the bell curve have higher fitness than those at the middle or other end of the curve.

16. Stabilizing Selection
Stabilizing selection occurs when individuals
near the center of the bell curve have higher
fitness then those at either end.

18. Disruptive selection
Disruptive selection occurs when individuals on the outer ends of the bell curve have higher fitness that those near the middle of the curve.

20. Genetic drift
The random change in allele frequency is called genetic drift.
Genetic Bottlenecks
When a small population allele’s frequency dramatically reduces due to some natural disaster or disease this is known as the bottle neck effect.

21. Founder effect
When an allele frequency changes as a result of migration of a small subgroup of a population this is known as the founder effect.
The founding individuals may carry different allele frequencies than the main population.

22. Evolution Versus Genetic Equilibrium
When there is no change in the allele frequencies the population is not evolving and this is known as genetic equilibrium.
Sexual Reproduction and Allele Frequency
Sexual reproduction, by itself, does not change the allele frequencies in a population. Hypothetically, sexually reproducing organisms could remain in genetic equilibrium.

23. Hardy-Weinburg principle
The Hardy-Weinberg principle states that the
allele frequency should stay constant unless one or more factors cause the frequency to change.
The Hardy Weinberg principle will
make predictions about allele frequency in a population using the following formula
p² + 2pq + q² = 1

24. p is defined as the frequency of the dominant allele and q as the frequency of the recessive allele for a trait controlled by a pair of alleles (A and a).
In other words, p equals all of the alleles in individuals who arehomozygous dominant (AA) and half of the alleles in people who are heterozygous (Aa) for this trait in a population.
p + q = 1

25. p = AA + ½Aa
q = aa + ½Aa or
(frequency of AA) + (frequency of Aa) + (frequency of aa) = 100%
And
(frequency of A) = (frequency of a) = 100%

26. (BB) p2 =(0.56)2=0.31=31% (bb) q2=(0.44)2=0.19=19%
Question: Suppose that in one generation the frequency for the allele B is 56% (p= 0.56)and the frequency of allele b is 44% (q=.44). If this population is at genetic equilibrium than we can predict what the percentage of each genotype for the next generation.
(BB) p2 =(0.56)2=0.31=31%
(bb) q2=(0.44)2=0.19=19%
(Bb) 2pq=2(.56)(.44)=.49=49%
If the population above does not show these predicted
phenotype frequencies, evolution is taking place

27. The Hardy Weinberg principle predicts five conditions that would disrupt the genetic equilibrium and cause evolution to occur:
Due to sexual selection, mates are chosen due to size, coloration, strength, etc. and do not mate randomly.
This works against equilibrium.

28. Genetic drift
Genetic drift can occur in small populations and cause evolutionary change
Gene flow occurs when individuals moving in or out of a population disrupt the genetic equilibrium.
Mutation in genes can disrupt allele frequencies causing evolution to occur.
Nature will select certain genotypes according to their fitness and this will disrupt genetic equilibrium and evolution will occur.

29. 17.3 The Process of Speciation
Isolating Mechanisms
A species is a population or group of populations that can interbreed and produce fertile off spring.
Speciation refers to the formation of a new species.
Reproductive isolation occurs when some members no longer interbreed with members of the population.
As a result of reproductive isolation the separated members can evolve into new species.

30. An example of speciation
The branching points on this partial Drosophila phylogeny represent speciation events that happened in the past.
sourcehttp://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_42

31. The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit...

32. Disaster strikes: A hurricane washes the bananas and the immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies mature and emerge from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them. At this point, speciation has not occurred — any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.

33. The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.

34. So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they've evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

35. Reproductive Isolation
Behavioural Isolation
When groups develop differences in courtship rituals or other behaviours
Eastern and Western Meadowlark look similar but
have different songs to attract mates.. Black and white sage
plants attract different pollinators and are different species

36. Geographic Isolation
Geographic barriers (rivers, canyons, mountains) separate two populations

37. Temporal Isolation
When two or more populations start to mate at different times

38. Darwin's Finches Founders Arrive
species M may have been blown on to the island and their allele frequencies
may have been different from the original
population

39. Geographic isolation
the islands environment was different from the
mainland and due to natural selection, founders effect, geographic isolation the island finch population developed
into a new species. A few birds went to another island and became geographically isolated.

41. Changes in gene pool
over time natural selection would have caused the populations on the two islands to evolve differently (beaks)
Behavioural isolation
some members may have made it back to the
original island but due to their differences they will not
mate with the original population. They are two distinct
species A and B.

42. Competition and continued evolution
the birds compete for natural resources and as a result their differences become greater.
Species B may evolve into a new species C.