1. Variation and Evolution Chapter 18 Pg – 196-204

2. Objectives At the end of this lesson you should be able to: 1.Define variation and mutation 2.List the causes of variations and mutations 3.List the types of mutations 4.Discuss the causes for and effects of increased mutation rates

3. Variation means there are differences between the members of a species. How would members of a species differ?

4. There are two types of variation a) Acquired variation is learned during life.

5. Examples of acquired conditions in humans are: language obesity athletic skills mental skills body building sun tan

6. Inherited Variation b) Inherited variation is caused by caused by sexual reproduction and by mutations.

7. Inherited Variation

8. Identical twins who were raised apart, Roger (left) and Tony first met at twenty-five and discovered they had many similarities. Photograph by Nancy

9. Causes of Inherited Variations 1.Sexual reproduction 2.Mutations

10. When your parents cells undergo meiosis to produce sperm/egg cells 8 million different combinations of their chromosomes are possible Every zygote is a 1 in 64,000,000,000,000 combination of chromosomes! This leads to great variation in species FACT

11. Whose Child?

12. Parents & Children

13. Offspring are similar to their parents but are not identical Cause – crossing over Differences between parents and offspring

14. Crossing Over

15. Fusion of gametes Sperm and egg cell fuse to form a zygote The combination of chromosomes leads to great variation in species

16. 1. What happens during meiosis? 2. What does meiosis lead to? 3. What are the causes of variation? 4. Why are offspring not identical to their parents? Learning Check

17. A mutation is a change in the amount or structure of DNA. Mutations can be either good, bad or have no effect at all. A good mutation can help an organism survive in a particular environment e.g. a mutation that causes better eyesight. This mutation will probably be passed onto offspring and help them survive also. Individuals without this mutation may not survive as well in the habitat and may eventually die out. Eventually all of the members of the species will have this mutation.

18. Causes of mutations: Mutations can occur naturally (spontaneous) or can be caused by mutagens. Mutagens are agents that cause mutations e.g. some types of radiation and some chemicals. Examples: Ionizing radiation such as x-rays, gamma rays, cosmic rays and ultra violet (UV) radiation. Chemicals such as formaldehyde, tobacco smoke, caffine, many drugs, pesticides and preservatives.

19. Types of Mutations A gene (or point) mutation is a tiny change in a single gene (often it only involves a single incorrect base). Examples: 1.Sickle cell anaemia 2. Cystic Fibrosis (inability to remove mucus from the lungs) 3. Albanism (lack of pigment melanin)

20. Sickle Cell Anaemia Inherited blood disorder Caused by mutation in the haemoglobin gene A person with two recessive copies of the recessive allele produces haemoglobin with one incorrect amino acid. This results in an insoluble form of haemoglobin that causes the red blood cells to be sickle (curved) shape. This causes red blood cells to clump and get trapped in smaller blood vessels Symptoms: paleness, weakness, heart failure severe pains, damage to brain & other organs and often death. Treatment: Blood transfusions Location: Southern Europeans & North Africans

21. Chromosome mutations Chromosome mutations are larger changes in the structure or number of one or more chromosomes. e.g. Down’s syndrome is caused by three number 21 chromosomes. The extra chromosome comes from the mother. It causes too much of a brain enzyme to be produced and causes the brain to form incorrectly.

22. Except for the X and Y, humans don’t survive with only 1 copy of any chromosome. Also, 3 copies is lethal in most cases. Chromosome Number Variations

23. Downs Syndrome

24. Dying for a Suntan Sunlight contains UV radiation (the component that causes a suntan) This can cause an abnormal cross link in DNA to form between certain adjacent bases. In most normal cases the cells can repair this damage, but sometimes a mutation can occur Unprotected exposure to UV radiation by the human skin can lead to skin cancer and extensive skin tumors.

25. Smoking A chemical in cigarette smoke causes mutations in a crucial gene associated with cancer. Cigarette smoke caused mutations in a gene called P53.

27. Learning Check 1. What is meant by aneuploidy? 2. Give an example? 3. What are the causes of structural variation in chromosomes? 4. Give an example of a structural variation? 5. What are the causes of mutations?

28. What have you learned Can you ……………… 1. Define variation and mutation 2. List the causes of variations and mutations 3. List the types of mutations 4. Discuss the causes for and effects of increased mutation rates

29. Evolution Evolution is the way in which living things change genetically to produce new forms of life over long periods of time.

30. Outline of the Theory of Natural Selection

31. H.M.S. Beagle Voyage

32. HMS Beagle made three voyages of exploration. 1826 - 1830: Leaves Plymouth on 22 May for first surveying voyage to Tierra del Fuego, South America. 1831 - 1832: Darwin joined the second voyage to South America and then around the world. 1837 - 1843: Third surveying voyage to Australia In the Galapagos Islands Darwin noticed how the same species of birds, cut off from centuries on different islands, had developed in quite different ways. This and many other amazing discoveries

33. Interesting Information Charles Darwin was born in England on the 12th of February 1809, he died on the 19th of April 1882. He is most famous for his work on natural selection, the idea that all species of life have evolved over time from common ancestors. This process involves favorable traits becoming more common in successive generations of living things while at the same time unfavorable traits become less common. Not only did Darwin develop the idea of natural selection, he also presented compelling evidence from his detailed research which included a five year voyage on the HMS Beagle. On this voyage, Darwin visited ecologically diverse regions such as Brazil, Chile, Australia, the Falkland Islands and the Galapagos Islands. His 1859 book ‘On the Origin of Species’, detailed much of his research on natural selection, it contained a large amount of evidence to back up his ideas and became a landmark work in the field of evolutionary biology. Darwin’s ideas created a lot of discussion regarding the impact on various scientific, religious and philosophical viewpoints.

34. Natural Selection Natural Selection is the process by which those organisms with genetically controlled characteristics that allow them to be well adapted to their environment will survive and reproduce to pass on their genes to the following generations. e.g. wolves & rabbits

35. Evidence for Evolution Comes from three main areas: 1. Study of fossils 2. Comparative anatomy (comparing structure of different organisms) 3. Study of embyros (4. DNA evidence – not on syllabus) We only need to study one of the above

36. Paleontology is the study of fossils. Fossils are generally rocks that have kept the shape of an organism. Fossils can be aged very precisely. About 98% of the organisms that ever lived have gone extinct.

39. Comparative anatomy – vertebrate limbs

40. Embryos and evolutionary history

41. DNA Evidence

42. Example of Evolution Evolution of the horse

43. Fossil record of modern horse is very well documented Covers a times pan of about 60 million years and involves many hundreds of species most of which are now extinct. Many trends have been noted in the evolution of the horse and we will look at one change: the height of the animal. Ancestor of modern horse developed 60 million years ago. They were about the height of a fox (0.4m)

44. Fossils from about 30 million yeas ago show that ancestors of the horse were larger about the size of a German Shepherd dog (0.6m) Fossils about 15 million years ago show the existence of a creature that was about the size of a Great Dane dog (1m) The modern horse evolved 1 million years ago and is normally (1.6m)

45. Hyracotherium Miohippus NeohipparionEquus