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Chapter 12: Sex Linkage and Polygenic Inheritance

Higher Human Biology. Unit 1: Cell Function and Inheritance. Chapter 12: Sex Linkage and Polygenic Inheritance. Learning intentions;. To revise sex chromosomes To examine effects of sex-linked genes To look at polygenic inheritance. The language – Lots. Polygenic Inheritance.

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Chapter 12: Sex Linkage and Polygenic Inheritance

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  1. Higher Human Biology Unit 1: Cell Function and Inheritance Chapter 12: Sex Linkage and Polygenic Inheritance Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  2. Learning intentions; • To revise sex chromosomes • To examine effects of sex-linked genes • To look at polygenic inheritance Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  3. The language – Lots........ Polygenic Inheritance Sex chromosomes Carriers Continuous variation Normal distribution Sex-linked Haemophilia Superscripts Allele Discontinuous variation Autosomes Additive Homozygous Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  4. 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 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  5. Normal Body Cells • In the nucleus of every body cell there are 46 chromosomes • 22 homologous pair (AUTOSOMES) and one pair of sex chromosomes Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  6. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  7. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  8. 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

  9. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  10. 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) Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  11. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

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

  13. Work out the genotypes of the following family tree Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  14. Answers • Carrier mother XCXc • Nomal father XCY • Normal daughter XCXC • Carrier daughter XCXc • Normal son XCY • Colour-blind son XcY Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  15. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  16. Colour blindness problem set http://www.biology.arizona.edu/human_bio/problem_sets/color_blindness/01q.html Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  17. Puzzle 1 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  18. Puzzle 1 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  19. Puzzle 2 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  20. Puzzle 2 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  21. Puzzle 3 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  22. Answer: Puzzle 3 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  23. Puzzle 4 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  24. Puzzle 4 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  25. Puzzle 5 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  26. Puzzle 5 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  27. Puzzle 6 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  28. Answer puzzle 6 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  29. Puzzle 7 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  30. Puzzle 7 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

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

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

  33. Puzzle 9 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  34. Puzzle 9 - answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  35. Puzzle 10 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  36. Puzzle 10 - Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  37. Puzzle 11 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  38. Puzzle 11 Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  39. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  40. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  41. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  42. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  43. When the father is normal and the mother is an unaffected carrier Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  44. Family Tree of Haemophilia Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  45. Puzzle 1 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  46. Puzzle 1- Answer Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  47. 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. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  48. Family Tree of Muscular Dystrophy • In this family the allele survives from female carrier to female carrier. Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  49. Polygenic Inheritance • Polygenic inheritance is a characteristic showing continuous variation and is controlled by the alleles of more than one gene • The more genes involved the more intermediate phenotypes that can be produced • The effects of the genes are additive (each dominant allele of each gene adds a contribution towards the characteristic controlled by the gene) Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

  50. Task: Torrance pg 91 Qu’s 1-3 Mrs Smith: Ch12 Sex Linkage and Polygenic Inheritance

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