Patterns of Evolution

1. Patterns of Evolution External 3 Credits

2. Do Now • Define the following terms; • Population • Species • Gene pool • Natural Selection

3. Answers • Population; is a group of individuals of the same species in an area. • Species; is a groups of individuals who normally interbreed to produce fertile offspring and who belong to the same gene pool. • Gene pool; all the alleles available to the population of a species. • Natural Selection; the process were the organsims with the best suited phenotype in a particular environment is select for (has increased survival)

4. Lesson Objectives • Review Yr 12 Evolution

5. A new idea? The idea that life has evolved is not new and goes back to the civilisations of the ancient Greeks. Christianity has a different perspective and is detailed in various passages in Genesis in the bible.

6. EVOLUTION • Macro-Evolution • Large changes in a gene pool over a long period of time, as in the formation of a new species, extiction and adaptive radiation • Micro-Evolution • Small changes in the frequency of alleles in a gene pool over successive generations

7. Write this down!!! Who evolves? • Individuals do not evolve – only populations evolve. • All the genes in a population are called a gene pool - the ratio of alleles and genotypes in a population can change over time. • As this changes, so evolution occurs.

8. Sources of Variation • Meiosis (covered in Yr 12) • Mutations Processes of Evolution • Genetic Drift • Founder Effect • Bottleneck Effect • Gene migration • Natural Selection

9. Meiosis • Independent Assortment • Segregation • Crossing over

10. What is a gene pool? Remember!! All the alleles present at all gene loci in all members of a population

11. GENE FLOW (results from Migration) • Individuals migrate between populations. • Immigrating individuals introduce new alleles. • Emigrating individuals remove alleles.

12. Gene flow can change a gene pool due to the movement of genes into or out of a population • Mutation changes alleles • Natural selection leads to differential reproductive success

13. Genetic Drift • A change in the gene pool of a small population due to chance • Genetic Bottleneck • Founder Effect

14. Originalpopulation Bottleneckingevent Survivingpopulation There are several potential causes of microevolution • Genetic drift is a change in a gene pool due to chance • Genetic drift can cause the bottleneck effect Figure 13.11A

15. Population bottleneck – genetic drift due to high mortality in a population. Unlikely that gene pool of the remaining population is representative of original population. Decreased genetic diversity among Cheetahs.

17. Cheetahs underwent 2 populationbottlenecks:1st during last ice age 2nd during nineteenth century due to excessive hunting.Today, just two isolated populations live in South & East Africa, numbering only in a few thousand animals between them. The South African cheetahs are so genetically alike that even unrelated animals can accept skin grafts from each other.

18. or the founder effect Figure 13.11B, C

19. Founder effect • Equivalent to genetic drift due to a few individuals leaving a large population to found a new group. • Unlikely that gene pool of founding population is representative of original population.

20. Founder effect Direction of movement Mainland Population Island Population 28 61% 4 44% 12 26% 5 56% 6 13%

21. Founder effect • Thus isolated populations of a species may have very different genes from the parent population and would therefore have a different susceptibility to the effects of natural selection on them at these new localities.

22. The Laysan Finch Story • Small population on Laysan Island and of conservation concern. • A group of 10 males and 10 females were captured and transported to a similar island 500 nm away. • They were individually marked and samples of their DNA were taken prior to release. • The introduced population thrived and samples of their DNA taken 5 years later showed a greater variation than the initial population. • How come?

23. Laysan Island 5 genes go with the original population. 500 nm New Island 2 new genes appear, giving a new total of 7 genes in the ‘new’ population.

24. Non-random Mating • Non-random mating causes certain alleles to become more common in future generations (some individuals leave more offspring than others).

25. Gene migration (Gene Flow) • Most populations are not closed systems. • Immigration from other populations brings in new gene combinations. • Those individuals, who leave the population (emigrate), take their genetic combinations with them. • I=in e=exit

26. Mutation • A change in the DNA - introduces ‘new’ alleles into the population. Mutations can be beneficial, have no effect (silent) or be harmful.

27. Increase or decrease of genetic diversity??? • Mutations and immigration increase genetic diversity. • Natural selection, emigration, non-random mating and genetic drift decrease genetic diversity. Important Slide!!!! Write this down!!!!!

28. Write this Down!! Natural Selection • The differential survival and reproductive success of organisms whose genetic traits- PHENOTYPES increase their chance to survive and reproduce in a particular environment. • It is considered to be the major driving force of evolution.

29. Natural Selection Summary • Over-production of young • Competition • Genetic Variation (ie different phenotypes) • Differential Fitness (Reproductive Success) • Fittest outcompete others to pass their “fit/favourable” genes onto their offspring • These “favourable” genes will then increase in frequency

30. Speciation • Speciation is the formation of a new species • Remember: A species is a group of organisms that normally interbreed in nature to produce fertile offspring & belong to the same gene pool • There are 2 types of speciation: • Allopatric Speciation • Sympatric Speciation

31. Allopatric speciation • Species can be allopatric – living in geographically different areas. Species B Species A

32. Sympatric species • Species can by sympatric – living together in the same geographical area. Species A & B live in all areas in the same geographical area.

34. The mechanism of speciation Allopatric speciation This is how most species come about. A single population occupying a uniform environment

35. Species undergoes an expansion of range Migration into new environments on the edge of the distribution Gives rise to subspecies as a result of different selection pressures. There is gene flow between all populations still.

36. Vegetation change River course change Selection the same Selection the same Further migration, environmental differences and the development of geographical barriers, gives rise to geographical isolation of some races and populations. This isolation halts gene flow between this and the original population.

37. Selection the same Selection different Different alleles being selected for. Some of the isolated populations develop genetic and chromosomal differences that no longer allow inter-breeding with the parent population. The subspecies is genetically and geographically isolated from its ancestral population.

38. Further changes in the environment remove the geographical barrier and allow the groups to live side by side. There is no interbreeding because some of the groups are now reproductively isolated, due to the different selection pressures they have been exposed to.

39. Gene flow can occur between these populations still as they have been exposed to the same selection pressures. There is NO gene flow between these populations now, because of different selection pressures resulting in Genetic changes.

40. These now become Sympatric and Allopatric populations

41. Allopatric Speciation – an example

45. The mechanism of speciation Sympatric speciation There are very few authenticated reports of speciation by this route. If it does occur, it happens within one generation. Starting with one population

46. A very small portion of the population undergoes a random mutation, which gives them instantaneous reproductive isolation from the rest of the species. It has to occur in a male and female in the same generation and must confer an immediate evolutionary advantage and separation from the parent population.

47. Polyploidy • This is the abrupt and almost instantaneous formation of a new species. • The main cause of this is a problem of separation of the chromosomes at Meiosis into the gametes and we will deal with it later on. • Rare in vertebrates but common in plants.

48. Aims for Today • To be able to explain the pre-zygotic and post-zygotic isolating mechanisms that lead to speciation.

49. Formation of species • Prevention of gene flow between populations can result in the formation of new species. • These are called isolating mechanisms. • There are pre and post-zygotic isolating mechanisms.

50. How does it happen? • Pre-zygotic isolating mechanisms prevent the fusion of gametes to form a zygote. • Post-zygotic isolating mechanisms prevent the zygote from developing further, if fertilization occurs.