1. Some Short Review What is a theory? Mutations (harmful, beneficial, neutral) Artificial Selection What are the evidences for evolution? – Age of the Earth – Fossil record – Biogeography – Homologous features – Analogous features – Vestigial Features

2. Some Short Review Darwin’s Theory and Adventures The Modern Synthesis (genetics + evolution) – Gene duplications – Pseudogenes Evolution acts on genes! Evolutionary Thinkers – Alfred Russel Wallace etc.

3. Some Short Review Natural Selection – Gathering Resources – Avoiding Predators – Adaptations to a Unique Environment Types of Selection – Directional – Stabilizing – Divergent Sexual Selection – Inter-sexual “male-male competition” – Intra-sexual “female choice”

4. Evolutionary Change without Selection

5. Natural Selection The way nature selects for some traits over others Selection is NOT random BUT evolutionary change doesn’t always happen this way

6. Change without Selection Changes within a gene pool can occur without the influence of successful traits These changes tend to reduce genetic diversity within a population

7. Change without Selection Change without selection occurs through genetic drift, the bottleneck effect, and the founder effect. Allele: a variation of a gene

8. Genetic Drift Genetic drift: The random shifting of the genetic make-up between generations – This shifting is entirely due to chance – So some generations may see more of a particular feature, and others may see less of that feature

9. Genetic Drift and Population Population size has a major effect on genetic drift Large populations tend to produce a stabilizing effect on alleles

10. Genetic Drift and Large Populations So in large populations, we expect to see a lot of genetic variability One trait may be more common in a generation, and less common in another generation Overall though, genetic variability remains fairly constant

11. Genetic Drift and Population A particular trait is more likely to become very common or to disappear in a small population

12. Genetic Drift and Small Populations So small populations tend to have less genetic variation Certain features become more common within that population, and certain features are lost

13. Variety and Large Populations So in order to maintain a high level of genetic variability, a large population is best Features remain in the population at a fairly constant level

14. Genetic Bottlenecks Bottleneck: A dramatic reduction in population size, usually resulting in significant genetic drift, due to catastrophe A population of 10000 that suddenly drops to 50 will experience a significant genetic bottleneck

15. How Does it Happen? A population reduction can occur in any number of ways: – Overhunting – Habitat loss – Natural disaster

16. How Does it Happen? The surviving population is likely to have a smaller gene pool than the initial population These particular traits will be passed along In this way, certain traits become favoured, while certain alleles disappear

17. As the Population Recovers If the population is allowed to recover, that population will be limited to those few traits left as a result of the bottleneck

18. Results of a Bottleneck Overall, a bottleneck reduces the size of the gene pool, and genetic variety This is generally harmful to the remaining population – Increased vulnerability to disease – Low reproductive success – Increased infant mortality

19. Cheetahs The cheetah species suffered a severe bottleneck about 10,000 years ago As few as 7 cheetahs survived, and all cheetahs today are descendents of these

20. Elephant Seals Population reduced to as few as 20 in the 1890s Today over 125,000 exist, but all are genetically very similar

21. The Founder Effect The Founder Effect: occurs when a small number of individuals separate from their original population and establish a new population

22. The Founder Effect The founding population would have a unique mix of alleles different than the larger original population By chance, some alleles that are less common in the larger population will be more common in the founding population

23. Frequency Differences Perhaps a rare variant of a gene occurs once in every 10000 people in the large population But in the founding population, that trait occurs in 1 of the 20 founders Original Population = 1/10000 (0.1%) Founding Population = 1/20 (5%) This represents an 50x increase in the frequency for that variant

24. Reduced Frequencies The founder effect leads to a population with a new, smaller, gene pool We can expect less variation within the new population

25. Founder Effect

30. The Galapagos Tortoise The entire population is the result of as few as one pregnant female tortoise from South America Her genes, and those of her offspring, formed the entire gene pool for the new Galapagos Tortoise population

31. The Amish Community A closed-off religious community that shuns the modern world Isolation has created a smaller gene pool within the Amish community

32. Bottlenecks vs. Founder Effect BottleneckFounder Effect Effect on Gene PoolSmaller Results in Genetic Drift? Yes How does it Happen? CatastropheSome individuals leave the population to start their own ExamplesCheetahs, Elephant Seals Galapagos Tortoise, Mennonites

33. A Mathematical Model for Evolution We can think of evolution as a change in the genetic makeup of a population We can also think about evolution from a math perspective: – The frequency of each allele in the population Can we predict the relationship between allele frequency and the chances of those frequencies remaining constant?

34. The Hardy-Weinberg Principle The Hardy-Weinberg Principle: states that in large populations where only random chance is at work, alleles should stay constant between generations

35. The Hardy-Weinberg Principle Other factors will result in evolution, as these will lead to changes in variant frequencies – Natural selection – Small population size – Mutation – Immigration or Emigration – Transfer of new alleles from a different species

36. Predicting Change By considering these factors, we can predict which populations are most likely to undergo the most evolutionary change

37. Applying the Principle to Different Species Some species will undergo evolutionary change faster than others A species with – High genetic diversity – Fast reproduction will respond to natural selection more quickly This is why bacteria develop resistance to antibiotics so quickly

38. Homework Questions Page 335 # 9, 10, 13