1. Mechanisms of Evolution

2. Mechanisms of Evolution
There are several:
Natural Selection
Gene Flow
Genetic drift
Mutations
Non-random mating

3. Artificial Selection
Domesticated breeds have not always been in their current form. This change has been achieved by repeatedly selecting for breeding the individuals most suited to human uses. This shows that selection can cause evolution.

6. Genetic Variation
Individuals in a species carry different alleles (An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.
Any change in gene (and allele) frequencies within a population or species is Evolution
Allele Frequency – proportion of gene copies in a population of a given allele

7. 1. Natural Selection:
Affects variation in a population as the better adapted (more fit) individuals to their environment survive and reproduce, passing on their genes to the successive generations increasing the frequency of favourable alleles in the population.
Nature “selects” which organisms will be successful

9. Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

10. Natural Selection

11. Dark Pepper Moths
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12. 4 Steps of Natural Selection:
1. In nature , more offspring are produced than can survive.
2. In any population, individuals have variation.
3. Individuals with advantageous variations survive and pass on their variations to the next generation.
4. Overtime, offspring with certain advantageous variations make up most of the population

13. 2. Gene Flow:
Is the movement of alleles into or out of a population (immigration or emigration).
Gene flow can introduce new alleles into a gene pool or can change allele frequencies.
The overall effect of gene flow is to counteract natural selection by creating less differences between populations.
Example:
Plant pollen being blown into a new area

14. Gene flow is what happens when two or more populations interbreed
Gene flow is what happens when two or more populations interbreed. This generally increases genetic diversity. Imagine two populations of squirrels on opposite sides of a river. The squirrels on the west side have bushier tails than those on the east side as a result of three different genes that code for tail bushiness. If a tree falls over the river and the squirrels are able to scamper across it to mate with the other population, gene flow occurs. The next generation of squirrels on the east side may have more bushy tails than those in the previous generation, and west side squirrels might have fewer bushy tails.

15. Gene Flow Some individuals from a population of brown beetles might
have joined a population of green beetles.
That would make the genes for brown beetles more frequent
in the green beetle population.

16. 3. Genetic Drift
The change in allele frequencies as a result of chance processes.
These changes are much more pronounced in small populations.
Directly related to the population numbers.
Smaller population sizes are more susceptible to genetic drift than larger populations because there is a greater chance that a rare allele will be lost.

17. Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift.

18. In a population of 100 bears, suppose there are two alleles for fur color: A1 (black) and A2 (brown). A1 has a frequency of .9, A2 a frequency of .1 (1.0 = 100%). The number of individuals carrying A2 is very small compared to the number of individuals carrying A1, and if only fifty percent of the population survives to breed that year, there's a good chance that the A2s will be wiped out.

19. Examples of Genetic Drift
A) The Founder Effect:
A founder effect occurs when a new colony is started by a few members of original population.
Small population that branches off from a larger one may or may not be genetically representative of the larger population from which it was derived.
Only a fraction of the total genetic diversity of the original gene pool is represented in these few individuals.

20. For example, the Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.

21. The Founder effect
Island
The Mainland

22. The Founder effect
Population
Island
The Mainland

23. The Founder effect The Mainland
A few individuals colonise a new isolated area
The Mainland

24. There may be a higher frequency of one allele in the founder population just by chance
This allele needn’t have been very common in the original population

25. The island population grows

26. …after a few generations
The green allele may be lost completely if individuals fail to leave offspring carrying it
Island

27. …after a few generations
The green allele may be lost completely if individuals fail to leave offspring carrying it
Island

28. …after a few generations
Mutations may occur creating new alleles
Island

29. …after a few generations
The new allele becomes more common
Island

30. The 2 populations now look very different!
Island
The Mainland

31. Some examples of the founder effect in action…
The Amish people, Pennsylvania
The Fugates of Kentucky

33. The Amish People 200 in founding population Within community marriages
Recessive conditions are common
Haemophilia
Dwarfism (1/14 carry the gene)
Still births/infant deaths
Physical deformaties

34. ‘The Royal Disease’
Haemophilia
The Tsars

35. The Fugates Small founding population Mountain communities
2 of the founders were carriers
of a recessive allele
Blue skin!

36. Examples of Genetic Drift
B) Population Bottleneck:
Occurs when a population undergoes an event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing.
The event may eliminate alleles entirely or also cause other alleles to be over-represented in a gene pool.
EX. Cheetahs

37. Cheetahs 10,000 years ago all but 1 species had died out
Severely threatened
Very low genetic diversity resulting in poor sperm quality among males
Females forced to breed with close relatives
Inbreeding generally decreases
the fitness of a population
(an inbreeding depression)

38. Bottleneck = any kind of event that reduces the population
significantly..... earthquake....flood.....disease.....etc.…

39. An example of a bottleneck:
Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000 but their genes still carry the marks of this bottleneck. They have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

41. Similarities Differences
Similarities and differences between the founder effect & bottlenecking
Similarities
Differences
Both are followed by genetic drift which results in changes in allele frequencies
In Bottlenecks individuals are killed, reducing the choice of mates, in the founder effect individuals are ecologically separated
Initially genetic diversity is lost in both systems
Both involve a small number of individuals breeding with each other, both may involve inbreeding among close relatives
Both may result in a new population which carries alleles that are unlikely to be a true representation of the original group

42. 4. Mutations Are inheritable changes in the genotype.
Provide the variation that can be acted upon by natural selection.
Mutations provide the raw material on which natural selection can act.
Only source of additional genetic material and new alleles.
Can be neutral, harmful or beneficial( give an individual a better chance for survival).
Antibiotic resistance in bacteria is one form.

43. Mutation is a change in DNA the hereditary material of life
Mutation is a change in DNA the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, and its physiology—all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life.
Somatic mutations occur in non-reproductive cells and won’t be passed onto offspring.
For example, the golden color on half of this Red Delicious apple was caused by a somatic mutation. The seeds of this apple do not carry the mutation.

44. The only mutations that matter to large-scale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germ line mutations.
A single germ line mutation can have a range of effects:
No change occurs in phenotype.

45. 2. Small change occurs in phenotype.
3. Big change occurs in phenotype.

Some really important phenotypic changes, like DDT
resistance in insects are sometimes caused by single
mutations.
A single mutation can also have strong negative effects for the organism.
Mutations that cause the death of an organism are called lethals — and it doesn't get more negative than that.

47. Causes of Mutations DNA fails to copy accurately.
External influences can create mutations.
Mutations can also be caused by
exposure to specific chemicals or
radiation.

49. 5. Non-Random Mating
In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behaviour.
Many plants self-pollinate, which is also a form of non-random mating (inbreeding).

50. Sexual reproduction results
in variation of traits in offspring
as a result of crossing over in
meiosis and mutations
Genetic shuffling is a source
of variation.

51. Sexual selection occurs when certain traits increase mating success.

52. There are two types of sexual selection.
intrasexual selection: competition among males
intersexual selection: males display certain traits to females