The language – Lots........

1. The language – Lots........ Polygenic Inheritance Sex chromosomes Carriers Continuous variation Normal distribution Sex-linked Haemophilia Superscripts Allele Discontinuous variation Autosomes Additive Homozygous

2. The stuff you Need to know! • Sex-linked inheritance and the effects of the presence of genes on the X-chromosome and not on the Y-chromosome. • Polygenic inheritance leading to characteristics

3. Normal Body Cells • In the nucleus of every body cell there are 46 chromosomes • 22 homologous pair (AUTOSOMES) and one pair of sex chromosomes

4. Female and Male Sex Chromosomes In the female, the sex chromosomes make up a fully homologous pair, the X chromosomes. In the male, the sex chromosomes make up a pair consisting of an X and a much smaller Y, which is homologous to only part of the X chromosome.

5. Sex-linked genes. • The X and Y chromosomes behave as a homologous pair at meiosis. However, the X chromosome differs from the Y chromosome in that the larger X carries many genes not present on the smaller Y. These genes are said to be sex-linked.

6. At fertilisation • When an X chromosome meets a Y chromosome at fertilisation, each sex-linked gene on the X chromosome becomes expressed in the phenotype of the human male produced. • This is because his Y chromosome does not possess alleles of any of these sex-linked genes and cannot offer dominance to them. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

7. Symbols Sex-linked genes • In crosses and family trees involving sex-linked gees, the sex chromosomes are represented by the symbols X and Y and the alleles of the sex-linked gene by appropriate superscripts.

8. X-linked recessive disorder - Red Green Colour Blindness • Inability to distinguish between red and green • A red green colour blind person does not see the number 29 on the right • In humans normal vision (C) is completely dominant to red-green colour blindness (c)

9. Genetics of Colour Blindness • Normal vision C • Red-green colour blindness c • These are the alleles are sex-linked because... • Heterozygous females are called carriers (Cc) Although they are unaffected themselves there is a 1 in 2 chance (50%) chance that they will pass the allele on to each of the offspring.

10. Five possible genotypes for normal and red-green colour blindness Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

11. Work out the genotypes of the following family tree

12. Answers • Carrier mother XCXc • Nomal father XCY • Normal daughter XCXC • Carrier daughter XCXc • Normal son XCY • Colour-blind son XcY

13. Why is colour blindness more common in males? • Red green colour blindness is rare in females since 2 recessive alleles must be inherited. • It is more common in males where only one is needed.

14. Colour blindness problem set http://www.biology.arizona.edu/human_bio/problem_sets/color_blindness/01q.html

15. Puzzle 1

16. Puzzle 1 - Answer

17. Puzzle 2

18. Puzzle 2 - Answer

19. Puzzle 3

20. Answer: Puzzle 3

21. Puzzle 4

22. Puzzle 4 - Answer

23. Puzzle 5

24. Puzzle 5 - Answer

25. Puzzle 6

26. Answer puzzle 6

27. Puzzle 7

28. Puzzle 7 - Answer

29. Puzzle 8 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

30. Puzzle 8 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

31. Puzzle 9

32. Puzzle 9 - answer

33. Puzzle 10

34. Puzzle 10 - Answer

35. Puzzle 11

36. Puzzle 11 Answer

37. Haemophilia: mutated form of factor VIII in platelets • Haemophiliacs cannot make the blood clotting protein Factor VIII. • This is a problem with blood clotting. So, if a tissue is damaged and blood vessels are broken, bleeding continues for longer than normal. • Some bleeding is obvious such as when the skin is cut or broken. Others are less easy to spot like bleeding into or around the joints.

38. X-linked recessive disorder -Haemophilia • It caused by a recessive allele carried on the X (e.g. The gene is located on the non-homologous region of the x-chromosome) but not the Y chromosome. • The haemophiliac allele (Xh)is recessive to the normal allele (XH). • Hence is sex-linked.

39. More common in males than females • Haemophilia is more common in men than women. • Fequency in britian is 1:5000 • Males inherit the allele from their mother and develop the disease. • Since (until recently) the prognosis for survival was poor and haemophiliac males did not survive to pass on the allele to their daughters (its on the X-chromosome). Therefore females with haemophilia where rare.

40. There is now treatment -FYI • ‘Clotting factor concentrates’ revolutionised haemophilia care allowing patients to travel, have jobs, and live full and independent lives. • Transfusion with whole blood and plasma.

41. When the father is normal and the mother is an unaffected carrier

42. Family Tree of Haemophilia

43. Puzzle 1

44. Puzzle 1- Answer

45. Muscular Dystrophy • Duchenne Muscular Dystrophy is the most common form of this disease. • Sufferers are severely disabled from an early age. • The normally die without passing allele onto the next generation. • Afects 1:3000 male infants. • Skeletal muscles loose their normal structure and fibrous tissue develops in their place. • Caused by a recessive allele carried on the X chromosome and is sex-linked.

46. Family Tree of Muscular Dystrophy • In this family the allele survives from female carrier to female carrier.

47. Y-linked Inheritance • Y-linked traits are controlled by alleles on the Y chromosome • Another word for Y-linked traits is holandric traits as they are “wholly male”.

48. Y-linked Inheritance • Do the words homozygous or heterozygous apply to Y-linked traits? • Are females affected by Y-linked traits?

49. What is this?

50. Y-linked Inheritance • An example of a Y-linked trait is . . . . . HAIRY EARS!