Polygenic Inheritance (AHL)

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Polygenic Inheritance (AHL)

  1. 1. Polygenic Inheritance (AHL)<br />Stephen Taylor<br />10.3 Polygenic Inheritance (AHL)<br />1<br />http://sciencevideos.wordpress.com<br />
  2. 2. Polygenic Inheritance<br />A single characteristic controlled by multiple genes. <br />10.3 Polygenic Inheritance (AHL)<br />2<br />http://sciencevideos.wordpress.com<br />
  3. 3. Polygenic Inheritance<br />A single characteristic controlled by multiple genes. <br />Polygenic inheritance gives rise to continuous variation in the phenotype. <br />Use these two examples in the exam. <br />Human Skin Colour<br />Wheat kernel colour<br />10.3 Polygenic Inheritance (AHL)<br />3<br />http://sciencevideos.wordpress.com<br />
  4. 4. Polygenic Inheritance<br />A single characteristic controlled by multiple genes. <br />Polygenic inheritance gives rise to continuous variation in the phenotype. <br />Use these two examples in the exam. <br />Human Skin Colour<br />Wheat kernel colour<br />Other examples: <br /><ul><li>Susceptibility* to heart disease, certain types of cancer, mental illnesses.
  5. 5. The Autism Spectrum. </li></ul>Autism is a pervasive developmental disorder that presents on a scale (known as the Childhood Autism Rating Scale). It is not as clearly polygenic as the above examples - it is suspected that gene interactions and environmental factors play a large role.<br />*susceptibility is not deterministic, but it is beneficial to know if you are at elevated genetic risk of these illnesses. <br />10.3 Polygenic Inheritance (AHL)<br />4<br />http://sciencevideos.wordpress.com<br />
  6. 6. Polygenic Inheritance of Skin Colour<br />Polygenic inheritance gives rise to <br />continuous variation in the phenotype.<br />Globally we observecontinuous variation in skin colours. Skin colour is the result of pigments, such as melanin, being produced - the darker the skin, the greater the protection against the harmful effects of the Sun. <br />Skin colour is though to be controlled by up to four <br />separate genes, each with their own alleles. This is too large for us to deal with simply, so we'll look at two genes with two alleles each. <br />Image from:<br />http://www.danacentre.org.uk/events/2007/05/03/259<br />10.3 Polygenic Inheritance (AHL)<br />5<br />http://sciencevideos.wordpress.com<br />
  7. 7. Polygenic Inheritance of Skin Colour<br />Polygenic inheritance gives rise to <br />continuous variation in the phenotype.<br />Globally we observecontinuous variation in skin colours. Skin colour is the result of pigments, such as melanin, being produced - the darker the skin, the greater the protection against the harmful effects of the Sun. <br />Skin colour is though to be controlled by up to four <br />separate genes, each with their own alleles. This is too large for us to deal with simply, so we'll look at two genes with two alleles each. <br />Image from:<br />http://www.danacentre.org.uk/events/2007/05/03/259<br />Watch this TED Talk and think about the following questions:<br /><ul><li>What is melanin and what purpose does it serve?
  8. 8. What skin tone were early humans most likely to have? Why does this change with latitude as humans migrated towards the poles?
  9. 9. What are the relative advantages and disadvantages of light and dark skin, depending on climate?</li></ul>TOK/ Aim 8: Why have people historically discriminated based on skin colour? How could the Natural Sciences educate people to think twice about their prejudices?<br />Nina Jablosnki breaks the illusion of skin colour, via TED. <br />http://www.ted.com/talks/lang/eng/nina_jablonski_breaks_the_illusion_of_skin_color.html<br />10.3 Polygenic Inheritance (AHL)<br />6<br />http://sciencevideos.wordpress.com<br />
  10. 10. Polygenic Inheritance of Skin Colour<br />Example: 2 genes (A and B), 2 alleles each<br />Assume: genes are not linked (separate chromosomes)<br />In polygenics, alleles can be: <br /><ul><li>Contributing (they add to the phenotype)
  11. 11. Non-contributing (they do not add to the phenotype)</li></ul>How many genotypes are possible?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />10.3 Polygenic Inheritance (AHL)<br />7<br />http://sciencevideos.wordpress.com<br />
  12. 12. Polygenic Inheritance of Skin Colour<br />Example: 2 genes (A and B), 2 alleles each<br />Assume: genes are not linked (separate chromosomes)<br />In polygenics, alleles can be: <br /><ul><li>Contributing (they add to the phenotype)
  13. 13. Non-contributing (they do not add to the phenotype)</li></ul>How many genotypes are possible?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />Remember that alleles segregate during meiosis. <br />Alleles of unlinked chromosomes orient randomly. <br />There is also random fertilisation of gametes. <br />So many combinations!<br />or<br />or<br />or<br />gametes<br />10.3 Polygenic Inheritance (AHL)<br />8<br />http://sciencevideos.wordpress.com<br />
  14. 14. Polygenic Inheritance of Skin Colour<br />Example: 2 genes (A and B), 2 alleles each<br />Assume: genes are not linked (separate chromosomes)<br />In polygenics, alleles can be: <br /><ul><li>Contributing (they add to the phenotype)
  15. 15. Non-contributing (they do not add to the phenotype)</li></ul>How many genotypes are possible?<br />Nine: <br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />Notice that the possible combinations of genotypes gives rise to continuous variation in the phenotype. <br />This population follows a normal distribution. <br />10.3 Polygenic Inheritance (AHL)<br />9<br />http://sciencevideos.wordpress.com<br />
  16. 16. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />Different colours?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />10.3 Polygenic Inheritance (AHL)<br />10<br />http://sciencevideos.wordpress.com<br />
  17. 17. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />Different colours?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />YES. <br />As long as they are non-identical twins. Two eggs will have been fertilised by individual sperm cells. <br />Each gamete carries a different combination of alleles, so it is possible that the twins have noticeably differently-coloured skin. <br />Couple has differently-coloured twins – for the second time! From Associated Press<br />http://www.youtube.com/watch?v=KgfObCmWJt4<br />10.3 Polygenic Inheritance (AHL)<br />11<br />http://sciencevideos.wordpress.com<br />
  18. 18. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />b. Lighter or darker than both parents?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />10.3 Polygenic Inheritance (AHL)<br />12<br />http://sciencevideos.wordpress.com<br />
  19. 19. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />b. Lighter or darker than both parents?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />F0<br />Phenotype:<br />AABb<br />AaBb<br />Genotype:<br />Punnet Grid:<br />F1<br />Genotypes:<br />Phenotypes:<br />10.3 Polygenic Inheritance (AHL)<br />13<br />http://sciencevideos.wordpress.com<br />
  20. 20. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />b. Lighter or darker than both parents?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />F0<br />Phenotype:<br />AABb<br />AaBb<br />Genotype:<br />Punnet Grid:<br />F1<br />Genotypes:<br />Phenotypes:<br />10.3 Polygenic Inheritance (AHL)<br />14<br />http://sciencevideos.wordpress.com<br />
  21. 21. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />b. Lighter or darker than both parents?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />F0<br />Phenotype:<br />AABb<br />AaBb<br />Genotype:<br />Punnet Grid:<br />F1<br />Genotypes:<br />Phenotypes:<br />10.3 Polygenic Inheritance (AHL)<br />15<br />http://sciencevideos.wordpress.com<br />
  22. 22. Polygenic Inheritance of Skin Colour<br />Is it possible for twins to be:<br />b. Lighter or darker than both parents?<br />Key to alleles:<br />A = add melanin<br />a = don’t add melanin<br />B = add melanin<br />b = don’t add melanin<br />YES. <br />F0<br />Phenotype:<br />AABb<br />AaBb<br />Genotype:<br />Punnet Grid:<br />darker<br />lighter<br />F1<br />Genotypes:<br />Phenotypes:<br />10.3 Polygenic Inheritance (AHL)<br />16<br />http://sciencevideos.wordpress.com<br />
  23. 23. Global Evolution of Skin Colour<br />Map of global skin colour distribution from:<br />http://en.wikipedia.org/wiki/Human_skin_color<br />What are the advantages of:<br />a. Dark skin in hot climates?<br />b. Pale skin in cold climates?<br />10.3 Polygenic Inheritance (AHL)<br />17<br />http://sciencevideos.wordpress.com<br />
  24. 24. Global Evolution of Skin Colour<br />Map of global skin colour distribution from:<br />http://en.wikipedia.org/wiki/Human_skin_color<br />What are the advantages of:<br />a. Dark skin in hot climates?<br />b. Pale skin in cold climates?<br />Protection against UV and therefore skin damage and cancer.<br />Increased production of vitamin D in low-sunlight conditions.<br />10.3 Polygenic Inheritance (AHL)<br />18<br />http://sciencevideos.wordpress.com<br />
  25. 25. Global Evolution of Skin Colour<br />Map of global skin colour distribution from:<br />http://en.wikipedia.org/wiki/Human_skin_color<br />What are the advantages of:<br />a. Dark skin in hot climates?<br />b. Pale skin in cold climates?<br /> In this case, the correlation between skin colour and latitude does suggest causality.<br />Protection against UV and therefore skin damage and cancer.<br />Dark-skinned people in cold climates should use vitamin D supplements. <br />Increased production of vitamin D in low-sunlight conditions.<br />Pale-skinned people in hot climates should slip-slop-slap-seek-slide. <br />10.3 Polygenic Inheritance (AHL)<br />19<br />http://sciencevideos.wordpress.com<br />
  26. 26. Polygenic Inheritance of Wheat Kernel Colour<br />Inheritance of colour of wheat kernels works in a similar way to human skin colour. <br />A wheat plant which is homozygous dominant for both genes is crossed with one which is heterozygous for both genes. What is the predicted ratio of phenotypes in the cross?<br />Key to alleles:<br />A = add red<br />a = don’t add red<br />B = add red<br />b = don’t add red<br />F0<br />Genotype:<br />Punnet Grid:<br />F1<br />10.3 Polygenic Inheritance (AHL)<br />20<br />http://sciencevideos.wordpress.com<br />
  27. 27. Polygenic Inheritance of Wheat Kernel Colour<br />Inheritance of colour of wheat kernels works in a similar way to human skin colour. <br />A wheat plant which is homozygous dominant for both genes is crossed with one which is heterozygous for both genes. What is the predicted ratio of phenotypes in the cross?<br />Key to alleles:<br />A = add red<br />a = don’t add red<br />B = add red<br />b = don’t add red<br />homozygous dominant <br />for both genes<br />F0<br />heterozygous for both genes<br />AaBb<br />AABB<br />Genotype:<br />Punnet Grid:<br />F1<br />10.3 Polygenic Inheritance (AHL)<br />21<br />http://sciencevideos.wordpress.com<br />
  28. 28. Polygenic Inheritance of Wheat Kernel Colour<br />Inheritance of colour of wheat kernels works in a similar way to human skin colour. <br />A wheat plant which is homozygous dominant for both genes is crossed with one which is heterozygous for both genes. What is the predicted ratio of phenotypes in the cross?<br />Key to alleles:<br />A = add red<br />a = don’t add red<br />B = add red<br />b = don’t add red<br />homozygous dominant <br />for both genes<br />F0<br />heterozygous for both genes<br />AaBb<br />AABB<br />Genotype:<br />Punnet Grid:<br />F1<br />10.3 Polygenic Inheritance (AHL)<br />22<br />http://sciencevideos.wordpress.com<br />
  29. 29. Polygenic Inheritance of Wheat Kernel Colour<br />Inheritance of colour of wheat kernels works in a similar way to human skin colour. <br />A wheat plant which is homozygous dominant for both genes is crossed with one which is heterozygous for both genes. What is the predicted ratio of phenotypes in the cross?<br />Key to alleles:<br />A = add red<br />a = don’t add red<br />B = add red<br />b = don’t add red<br />homozygous dominant <br />for both genes<br />F0<br />heterozygous for both genes<br />AaBb<br />AABB<br />Genotype:<br />Punnet Grid:<br />“All AB”<br />F1<br />Phenotype ratio: 1 very red: 2 Red: 1 pink<br />10.3 Polygenic Inheritance (AHL)<br />23<br />http://sciencevideos.wordpress.com<br />
  30. 30. Mathematical Questions<br />A trait is controlled by two genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />10.3 Polygenic Inheritance (AHL)<br />24<br />http://sciencevideos.wordpress.com<br />
  31. 31. Mathematical Questions<br />Key to alleles:<br />A = contributing<br />a = non-contributing<br />B = contributing<br />b = non-contributing<br />A trait is controlled by two genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />Same!<br />There are 16 combinations of parent alleles, making 9 different genotypes.<br />10.3 Polygenic Inheritance (AHL)<br />25<br />http://sciencevideos.wordpress.com<br />
  32. 32. Mathematical Questions<br />Key to alleles:<br />A = contributing<br />a = non-contributing<br />B = contributing<br />b = non-contributing<br />A trait is controlled by two genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />2<br />4<br />3<br />1<br />0<br />There are 16 combinations of parent alleles, making 9 different genotypes.<br />These make up 5 different phenotypes. <br />10.3 Polygenic Inheritance (AHL)<br />26<br />http://sciencevideos.wordpress.com<br />
  33. 33. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />10.3 Polygenic Inheritance (AHL)<br />27<br />http://sciencevideos.wordpress.com<br />
  34. 34. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />10.3 Polygenic Inheritance (AHL)<br />28<br />http://sciencevideos.wordpress.com<br />
  35. 35. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />10.3 Polygenic Inheritance (AHL)<br />29<br />http://sciencevideos.wordpress.com<br />
  36. 36. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />Phenotypes = 7<br />10.3 Polygenic Inheritance (AHL)<br />30<br />http://sciencevideos.wordpress.com<br />
  37. 37. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes & phenotypes are possible for this trait? <br />Genotypes = 33<br />Phenotypes = 7<br />10.3 Polygenic Inheritance (AHL)<br />31<br />http://sciencevideos.wordpress.com<br />
  38. 38. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes are possible in a cross between a homozygous dominant male and a homozygous recessive female?<br />10.3 Polygenic Inheritance (AHL)<br />32<br />http://sciencevideos.wordpress.com<br />
  39. 39. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes are possible in a cross between a homozygous dominant male and a homozygous recessive female?<br />homozygous recessive<br />Phenotype:<br />homozygous dominant<br />aabb<br />AABB<br />Genotype:<br />10.3 Polygenic Inheritance (AHL)<br />33<br />http://sciencevideos.wordpress.com<br />
  40. 40. Mathematical Questions<br />Key to alleles:<br />A, B, C = contributing<br />A, b, c = non-contributing<br />A trait is controlled by three genes, each with two alleles.<br />How many genotypes are possible in a cross between a homozygous dominant male and a homozygous recessive female?<br />homozygous recessive<br />Phenotype:<br />homozygous dominant<br />aabb<br />AABB<br />Genotype:<br />Punnet Grid:<br />Only one possible genotype!<br />10.3 Polygenic Inheritance (AHL)<br />34<br />http://sciencevideos.wordpress.com<br />
  41. 41. For more IB Biology resources:<br />http://sciencevideos.wordpress.com<br />This presentation is free to view. Please make a donation to one of my chosen charities at Gifts4Good and I will send you the editable pptx file.<br />Click here for more information about Biology4Good charity donations. <br />10.3 Polygenic Inheritance (AHL)<br />35<br />This is a Creative Commons presentation. It may be linked and embedded but not sold or re-hosted. <br />

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