Talkie Time and recap

1. Talkie Time and recap

2. Lesson 7: Mechanismsof Evolution

3. Objective:Explain the mechanisms that produce change in populations from generation to generation (e.g.,artificial selection, natural selection, genetic drift, mutation, recombination) -STEM_BIO11/12-IIIc-g-9

4. (20 mins) Film Viewing (Mechanism of Evolution) https://www.youtube.com/watch?v=7sxgrpFrlpk Guide: In a Group, list down the mechanisms of evolution and in a table form provide characteristics or description for each mechanism. Choose a presenter

5. Mechanisms of Evolution There are several: • Artificial Selection • Natural Selection • Gene Flow • Genetic drift • Mutations • Non-random mating/Recombination

6. 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.

9. 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 positionon 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

10. 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

12. 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.

13. Natural Selection

14. Dark Pepper Moths • http://www.youtube.com/watch?v=LyRA807djLc&feature=related

15. 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

16. Natural Selectionvs.Selective Breeding Environmental and Human Influences Natural selection and selective breeding can both produce changes in animals and plants. The difference between the two is that natural selection occurs in nature, but selective breeding only occurs when humans intervene.

17. Why are we learning about this? • Living organisms are dependent on the environment and other species for their survival. • Because we are all part of a giant food web, changes in one part of the web can have a big impact on other parts of the web. • When one food source disappears, a predator will have to find another food source in order to survive.

18. Natural Selection Selective Breeding • Process by which organisms that are best suited to their environment survive and reproduce most successfully. • Method of breeding that allows only those organisms with desired characteristics to produce the next generation. Natural Selection vs. Selective Breeding

19. IN OTHER WORDS… Natural Selection Selective Breeding • Process of selection whereby favorable traits become more common and less favorable traits become less common in following generations. • A form of artificial selection whereby deliberate breeding results in desired traits in plants and animals Selected by Nature vs. Selected by Humans

20. Natural Selection Example: White Colored vs Dark Colored Peppered Moths during the Industrial Revolution • Manchester, England from 1845 to 1890. • Before the industrial revolution, the trunks of the trees in the forest around Manchester were light grayish-green due to the presence of lichens.

21. What the industrial revolution may have looked like. • “

22. Can you see the moths? • Most of the peppered moths in the area were light colored with dark spots. • As the industrial revolution progressed, the tree trunks became covered with soot and turned dark. • Over a period of 45 years, the dark variety of the peppered moth became more common. • Why?

23. Peppered Moths Survival of the strongest? NO Survival of the fittest –the organism best fit for the environment may survive and pass its favorable adaption/variation down to the next generation. Example: Darker moths were now better hidden from predators and survived in greater numbers, living to reproduce, pass their now favorable trait on and continue to increase in numbers.

24. Natural Selection • Individuals in a species show a wide range of variation because of differences in their genes • Genes that allow individuals to survive are then passed on to their offspring) • Individuals poorly adapted are less likely to survive, reproduce, and pass on their genes

25. Natural Selection and Horses

26. Early Horse (Eohippus) • lived 55-60 million years ago • lived in forests and ate leaves • about the size of a fox • 4 toes to walk on soft forest floor Modern Horses (Equus) • began to develop 2 million years ago • as a result of changes in the global climate, lived in grasslands and ate grass • developed long legs and one toe (hoof) to help the horse run faster from predators and longer teeth to eat the grass

27. Galapagos Islands • 1850’s: Charles Darwin described how organisms might change over time. • 5 years of observations on the islands.

28. Galapagos Finches

29. Selective breeding Human Influence on characteristics and behavior. • Domestic Animals • Ex: Chickens, Dogs, Cows, Horses • Plants: • Ex: Corn, Wheat, Fruit hybrids

30. These are the steps in selective breeding: • Decide which characteristics are important • Choose parents that show these characteristics • Select the best offspring from parents to breed the next generation • Repeat the process continuously

31. Domestic Animals

32. Selective Breeding of Horses • Ancient Wild Horses Help Unlock Past Aug. 23, 2011 — An international team of researchers has used ancient DNA to produce compelling evidence that the lack of genetic diversity in modern stallions is the result of the “domestication” process. • Horses were first domesticated for transportation, agricultural work and warfare • Today they are also bred for racing and companionship

34. Different varieties of dog have been produced over many generations by selective breeding. • For example, pedigree dogs come in lots of different varieties, called breeds of dog. They may be different colors and sizes, but they are all still dogs. They are all still the same species. Different breeds of dogs http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/variation_classification/revision/5/ (click on the link and read about selective breeding of cows and other examples of selective breeding)

36. Cows-bred for meat or milk The picture above shows a dairy cow. She has been bred for milk. She has been selectively bred to produce enough milk for ten calves, but her calf is removed from her shortly after birth. Most cows are only milked twice a day. It may have to carry over 20 liters of milk. Many cows go lame through carrying all this milk. The cow above has been selectively bred for meat. She produces enough milk to feed one calf. Her calf will milk her six times per day. She only needs a small udder.

37. Aberdeen Angus bull - bred for beef Friesan cow - dairy breed

38. Selective Breeding of Farm AnimalsChickens - bred for eggs or meat The chickens on the left are egg-laying hens. They have been selectively bred to lay lots of eggs, but they grow at a normal rate. Most are still kept in battery cages, though this system is to be banned in 2012. The chickens on the right are broiler chickens. They have been bred for meat. They grow twice as quickly and are usually slaughtered at six weeks old. Most meat chickens are kept intensively in large sheds. You can click on the link to read more about these chickens. http://www.ciwf.org.uk/includes/documents/cm_docs/2008/s/science_worksheets_selective_breeding.pdf

39. Hybrid Fruits a peach/apricot/plum hybrid. The mellow-tasting fruit has the texture of a peach, but tastes like a blend of plum and apricot. • Nectarcots • Pluots • Peacotums

40. 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

41. 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.

42. 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.

43. 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.

44. 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.

45. 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.

46. 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.

47. 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.

49. 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 http://www.nytimes.com/1985/09/17/science/loss-of-gene-diversity-is-threat-to-cheetahs.htm l

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