1. Variations and Mutations

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

3. Chromosomes and Genetics
Chromosomes are long pieces of DNA, with supporting proteins
Genes are short regions of this DNA that hold the information needed to build and maintain the body
Genes have fixed locations: each gene is in a particular place on a particular chromosome
Diploids have 2 copies of each chromosome, one from each parent. This means 2 copies of each gene.

4. Human Chromosomes We have 46 chromosomes, or 23 pairs.
44 of them are called autosomes and are numbered 1 through 22. Chromosome 1 is the longest, 22 is the shortest.
The other 2 chromosomes are the sex chromosomes: the X chromosome and the Y chromosome.
Males have and X and a Y; females have 2 X’s: XY vs. XX.

5. Male Karyotype

6. Female Karyotype

7. Sex Determination
The basic rule: If the Y chromosome is present, the person is male. If absent, the person is female.

8. Meiosis
the X and Y chromosomes separate and go into different sperm cells:
½ the sperm carry the X and the other half carry the Y.
All eggs have one of the mother’s X chromosomes
The Y chromosome has the main sex-determining gene on it, called SRY

9. Sex Determination
About 4 weeks after fertilization, an embryo that contains the SRY gene develops testes, the primary male sex organ.
The testes secrete the hormone testosterone.
Testosterone signals the other cells of the embryo to develop in the male pattern.

10. Learning Check What is the difference between a chromosome and a gene?
What is the difference between the terms haploid and diploid?
How many pairs of chromosomes do we have?
What are pair number 23 called?
What is the difference between the male and the female karyotype?

11. Causes of Inherited Variations
Sexual reproduction (fusion of gametes)
Crossing Over during Meiosis – this allows genes to move between chromosomes
Mutations
The independent assortment of chromosomes when gametes are being formed

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

13. Fact
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

14. But why do some children look a lot like their parents?
On the next slide try to match up the parent with their child.
In some cases its quite easy. Why?

15. Whose Child?

16. Whose Child?

17. Differences between parents and offspring
Offspring are similar to their parents but are not identical
Cause – crossing over
Before one of the pairs of chromosomes are passed on into the gamete(sex cell like sperm or egg) they undergo crossing over. See next slide

18. Either one of these ends up in the sex cell
Crossing Over
Either one of these ends up in the sex cell

19. Learning Check What happens during meiosis? What does meiosis lead to?
What are the causes of variation?
Why are offspring not identical to their parents?

20. Mutations
The last few slides explain how mutations can cause variation

21. Chromosome Number Variations
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.
Down Syndrome is the most common human aneuploidy. It is also called trisomy-21, meaning 3 copies of chromosome number 21.

22. Aneuploidy

23. Downs syndrome

24. Chromosome Structure Variations
Chromosomes can be broken by X-rays and by certain chemicals.
The broken ends spontaneously rejoin, but if there are multiple breaks, the ends join at random.
This leads to alterations in chromosome structure.

25. Structure Variation Examples
There are lots of ways chromosomes can change structure, so the syndromes are not as well defined as with number variations.

26. Point mutations These are changes in just one base pair of a gene.
If a point mutation occurs in a gamete or in a cell that gives rise to gametes, it may be transmitted to offspring and to a succession of future generations e.g. sickle cell anaemia.
© Biology Support Service 2007

27. Sickle Cell Anaemia is caused by a point mutation-
A mutation of a single base pair in the gene that codes for one of the polypeptides of haemoglobin.

28. Just one amino acid could affect how a protein folds
Protein folding
Campbell and Reece (2002) Biology
Just one amino acid could affect how a protein folds
© Biology Support Service 2007

29. As a result, damage is caused to the red blood cell membrane, resulting in a cellular lifespan of only a few days. Due to the sickle cell shape, small capillaries may become blocked.
ww.sciencemuseum.org.uk/genes/223.asp

30. Missing part of Chromosome 5
Cri Du Chat Syndrome
Cri-du-chat syndrome comes from a deletion of one end of chromosome 5, so the person only has 1 copy of all the genes on this end of the chromosome.
Missing part of Chromosome 5

31. Mutations – Other Causes
Radiation High energy radiation from a radioactive material or from X-rays
These X rays attack the DNA molecule and alters it in many ways.
Radiation can also cause double strand breaks in the DNA molecule, which the cell's repair mechanisms cannot put right
Remember Chernobyl

32. 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.

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

36. Learning Check What is meant by aneuploidy? Give an example?
What are the causes of structural variation in chromosomes?
Give an example of a structural variation?
What are the causes of mutatoins?

37. What have you learned? Can you ……………… Define variation and mutation
Define variation and mutation
List the causes of variations and mutations
List the types of mutations
Discuss the causes for and effects of increased mutation rates

38. The Theory of Natural Selection and the Survival of the Fittest
Evolution
The Theory of Natural Selection and the Survival of the Fittest

39. Lesson Objectives Define evolution
At the end of this lesson you should be able to
Define evolution
Outline the Darwin and Wallace Theory of natural selection
Discuss the evidence of evolution from either fossil, comparative anatomy or the study of embryos. (Fossil evidence was chosen for this unit)

40. Evolution
Evolution is the changing of one species into another that takes place through natural selection
It takes place over a long period of time

41. Darwin And Wallace
Darwin presented the theory of evolution by natural selection in 1858
Much of Darwin’s work was done on the Galapagos islands
Darwin proposed a mechanism for evolution by natural selection
Alfred Wallace working in Borneo also proposed the same theory

42. Observations made by Darwin
Over breeding
Population numbers remain constant
Inherited variations occur in populations

43. Conclusions drawn by Darwin
There is a struggle for existence
- competition will occur
Natural Selection
- only the fittest will survive

44. The Mechanism of Evolution
Too many offspring are produced
This leads to competition
All populations have genetic variations
Individuals that are best adapted to the environment survive
As the environment changes new adaptations emerge
Over a long period of time a new species forms

45. Learning Check Define Evolution
Who were the two people who proposed the theory of evolution
Where did Darwin carry out his work?
What were the observations and conclusions made by Darwin?
Outline the mechanism of evolution

46. Evidence for Evolution
The fossil Record
Palaeontology is the study of fossils.
A fossil is the remains of an organism
Fossils can be dated using radioactive carbon

47. Fossils Fossils show changes compared to modern organisms
Some fossil organisms are extinct
Modern fossils show increased complexity
Fossil evidence can be linked to environmental change

48. Dinosaurs 65 million years ago dinosaurs became extinct
Iridium an element found in meteorites was laid down
This would suggest that a large meteorite hit earth creating large amounts of rock dust.
This dust led to the earth becoming colder and darker causing plants and animals to become extinct.

49. Evolution of the horse
The ancestor of the modern horse evolved 60 million years ago
Horse Fossils were 0.4m tall
30 million years ago
Horse fossils were 0.6m tall
15 million years ago
Horse fossils were 1m tall
1 million years ago
Equus – the modern horse evolved
Horse fossils were 1.6m tall

50. Miohippus
Hyracotherium
Neohipparion
Equus

53. Learning Check Outline the evidence for evolution
How do fossils provide evidence for evolution
Can you outline the evolution of the modern horse?

54. What have you learned? Define evolution
Can you…………………………
Define evolution
Outline the Darwin and Wallace Theory of natural selection
Discuss the evidence of evolution from the study of fossils

55. End