1. Exam question(2008)
During the process of meiosis, independent assortment and crossing over (recombination) can occur. This results in genetic variation in the offspring of sexually reproducing individuals
Describe what happens during independent assortment
Explain how crossing over (recombination) can contribute to the genetic variation that results from sexual reproduction. You may wish to draw a diagram.
Genetic variation can be a results from mutation. Explain the results of mutation sin somatic and gametic cells

2. EVOLUTION
MAH – Year 12

3. DO NOW What is the gene pool?
Where does the variation originally come from?
What is gene flow?

4. Summary

5. Evolution Intro
...process by which new species of plants and animals develop from earlier forms
...is the change in the gene pool of a population over periods of time and occurs whenever the frequency of alleles in the gene pool changes
... is the change in the inherited traits of a population of organisms through successive generations

6. Homerman

7. Gene Pools and Allele Frequencies
What is the gene pool?
Is the total number of genes and alleles present within a population at a given point in time

8. Allele Frequency Frequency of allele = Occurrence of that allele
Total number of alleles
Take two bits of paper either a pink/green (or beans)
We will use this to show how allele frequencies can change

9. Frequency of allele = Occurrence of that allele
Total number of alleles

10. Simulation
Sickle Cell and Malaria Simulation

11. Gene Pools and Allele Frequency
VARIATION IN GENE POOL DUE TO MUTATIONS AND RECOMBINATION
IMIGRATION AND EMIGRATION
Gene Pool 1
GEOGRAPHICAL BARRIERS THAT AFFECT GENE FLOW
Gene Pool 2
GENE FLOW: Genes are exchanged with other gene pools as individuals move between them. This is a source of new genetic variation and tends to reduce differences between populations due to natural selection or genetic drift

13. Gene Pool Change Factors Favouring Gene Pool Stability
Factors Favouring Gene Pool Change
Large Population
Small Population
Random Mating
Assortative mating (like and like)
No gene flow
Gene Flow (immigration and emigration)
No Mutation
Mutations
No Natural Selection
Natural Selection

14. Evolution, Alleles, and Gene Pools
Variation within a gene pool comes from mutation or recombination
Changes in allele frequencies proceed EVOLUTION
Changes in allele frequency come from immigration and emigration (gene flow), genetic drift (CHANCE), natural selection, sexual selection

15. Crossing Over

16. Gene Migration
Is the introduction or loss of alleles into or out of a population
Immigration: when individuals migrate INTO a population they bring new alleles into the gene pool
Emigration: When individuals migrate OUT OF a population they remove some of the alleles from the gene pool
New alleles introduced into a gene pool INCREASE S THE GENETIC VARIATION of a population  more likely to survive changes in the environment
Diagram to match with a gene pool
Make some alleles

17. Genetic Drift
...is the change in allele frequency in a gene pool in a small population by CHANCE alone
e.g. The death of an individual carrying a rare allele will make the frequency of that allele less or removed all together
Special cases: Founder and Bottleneck

18. Founder Effect
...occurs when a few individuals migrate from a larger population to establish a new population in a new area Consequence: The colonising population may evolve differently from that of the parent population In some cases: it may be possible for certain alleles to be missing altogether from the individuals in the isolated population.

19. Polydactyly Fingers
Polydactyly -- extra fingers or sometimes toes -- is one symptom of Ellis-van Creveld syndrome. The syndrome is commonly found among the Old Order Amish of Pennsylvania, a population that experiences the "founder effect."

20. Why??
Genetically inherited diseases like Ellis-van Creveld are more concentrated among the Amish because they marry within their own community.
This prevents new genetic variation from entering the population.
Children are therefore more likely to inherit two copies of the particular recessive genes that lead to genetic disease.

22. Founder and Huntington’s
Huntington’s is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and dementia
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.

23. Another example
Milk A1/A2 Protein

24. Bottleneck Effect
...occurs when a population is reduced to low numbers by predation, disease, periods of climate change, or catastrophe (selection pressures of natural disasters) The populations recover after being squeezed through a ‘bottleneck’ of low numbers Results in some alleles being above normal number or lost altogether (loss of genetic variation) Pg. 105 Biozone

27. Example of 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.

28. Example of Bottleneck
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.

29. Non-random Mating Nearby mating  lead to inbreeding (song)
The ultimate of inbreeding is self-fertilisation (occurs in plants)
Inbreeding
Results in homozygous alleles – heterozygous advantage lost
Chance of unfavourable recessive genes turning up in the offspring is enhanced – humans have strict rules against incest

30. Natural Selection
...is the environment selecting FOR or AGAINST certain PHENOTYPES
phenotypes: structure, metabolism, behaviour, physiology
environment factors: predators, competition, disease, lack of food, light, water, climate factors
..possess adaptations such as ability to avoid predators or to compete strongly for food
BEAN EXPERIMENT

31. Natural Selection
...can act on phenotypes in different ways that will either maintain or change the genotypes present in a species

33. Population Size

34. Allopatric speciation
Is just a fancy name for speciation by geographic isolation
Speciation: The formation of new and distinct species in the course of evolution

35. Allopatric speciation
In this mode of speciation, something extrinsic to the organisms prevents two or more groups from mating with each other regularly, eventually causing that lineage to speciate.
Isolation might occur because of great distance or a physical barrier, such as a desert or river.

36. Allopatric speciation (cont)
In order for a speciation even to be considered “allopatric,” gene flow between the soon-to-be species must be greatly reduced—but it doesn’t have to be reduced completely to zero.

38. Steps Involved:
A single randomly mating species is widely distributed through a geographical region.
Quite suddenly, a natural barrier forms, dividing the species into two separate groups.
Over the succeeding generations, either through selection or random events, the two populations come to differ.
When the barrier is removed, the populations are now so different that there is no reproduction between them: they have become two distinct species

39. Example:
Geographic patterns: If allopatric speciation happens, we’d predict that populations of the same species in different geographic locations would be genetically different. There are abundant observations suggesting that this is often true.
For example, many species exhibit regional “varieties” that are slightly different genetically and in appearance, as in the case of the Northern Spotted Owl and the Mexican Spotted Owl.

41. Question?
On the Galapagos islands Charles Darwin noticed a large variety of finches which differed in beak shape and overall size.
WHY WOULD INDIVIDUALS ON THE SAME ISLAND OR NEARBY ISLANDS HAVE DIFFERERNT BEAK SHAPES AND SIZES?

42. THIS IS ADAPTIVE RADIATION AND NATURAL SELECTION AT WORK
Question?
On the Galapagos islands Charles Darwin noticed a large variety of finches which differed in beak shape and overall size.
WHY WOULD INDIVIDUALS ON THE SAME ISLAND OR NEARBY ISLANDS HAVE DIFFERERNT BEAK SHAPES AND SIZES?
THIS IS ADAPTIVE RADIATION AND NATURAL SELECTION AT WORK

43. Adaptive radiation (defined…)
This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection.
The development of many different forms from an originally homogeneous group of organisms as they fill different ecological niches

45. This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection

46. Example: Finches
Finches managed to occupy the Galapagos islands, over 600 miles away from their original location. They occupied an ecological niche with little competition.
As the population began to flourish in these advantageous conditions, intraspecific competition became a factor, and resources on the islands were squeezed and could not sustain the population of the finches for long.
Due to the mechanisms of natural selection, and changes in the gene pool, the finches became more adapted to the environment.
As competition grew, the finches managed to find new ecological niches, that would present less competition and allow them, and their genome to be continued.
The finches adapted to take advantage of the various food sources available on the island, which were being used by other species. Over the long term, the original finch species may have disappeared, but by diversifying, would stand a better chance of survival.
All in all, the finches had adapted to their environment via natural selection, which in turn, has allowed the species to survive in the longer term, the prime directive of any species.

47. Adaptive Radiation

48. Patterns of Evolution

51. Divergent Evolution
Divergent evolution is the process of two or more related species becoming more and more dissimilar.
Example: The red fox and the kit fox provide and example of two species that have undergone divergent evolution. The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees. The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators. The ears of the kit fox are larger than those of the red fox. The kit fox's large ears are an adaptation to its desert environment. The enlarged surface area of its ears helps the fox get rid of excess body heat. Similarities in structure indicate that the red fox and the kit fox had a common ancestor. As they adapted to different environments, the appearance of the two species diverged.

52. Different Environments
Divergent Evolution
Less Alike
Different Environments
Related Species
Related Species

53. Convergent Evolution
Convergent evolution - unrelated species become more and more similar in appearance as they adapt to the same kind of environment.
Example: unrelated types of plants that have adapted to desert environments. The Cactus which grows in the American desert has similar resemblances to the euphorbia, which grows in the African deserts. Both have fleshy stems armed with spines. These adaptations help the plants store water and ward off predators.

54. Convergent
Bird and bat wings are analogous—that is, they have separate evolutionary origins, but are superficially similar because they evolved to serve the same function. Analogies are the result of convergent evolution.

55. Convergent Evolution Unrelated Species Unrelated Species
Similar Environments
More Alike