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Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation
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Chapter 19 Heredity Lesson 5 - Discontinuous and Continuous Variation

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  • 1. Discontinuous and Continuous Variation
  • 2. Lesson Objectives <ul><li>(j) describe the difference between continuous and discontinuous variation and give examples of each </li></ul><ul><li>(k) state that competition which arises from variation leads to differential survival of, and reproduction by, those organisms best fitted to the environment </li></ul><ul><li>(l) give examples of environmental factors that act as forces of natural selection </li></ul><ul><li>(m) assess the importance of natural selection as a possible mechanism for evolution </li></ul><ul><li>(n) give examples of artificial selection such as in the production of economically important plants and animals </li></ul>
  • 3. Variations <ul><li>Variations are differences in traits of characteristics between individuals of the same species </li></ul><ul><li>Discontinuous variations e.g. Mendel’s pea plants either tall or short and had no intermediate forms between these traits </li></ul><ul><li>Easily distinguishable and not affected by environmental conditions </li></ul><ul><li>Brought about by one or a few genes </li></ul>
  • 4. Continuous variation <ul><li>When traits do not fall into clear-cut classes </li></ul><ul><li>e.g. intermediate skin colour and height </li></ul><ul><li>There is a continuous variation from one extreme to the other </li></ul><ul><li>This is brought about by </li></ul><ul><li>the additive (combined) </li></ul><ul><li>effect of many genes e.g. </li></ul><ul><li>more dark genes than </li></ul><ul><li>fair genes the darker the </li></ul><ul><li>skin tone </li></ul>
  • 5. Modified by environmental conditions, e.g. greater exposure of the skin to sunlight will produce a darker skin colour Not modified by environmental changes Genes show additive effect , e.g. the more ‘dark’ genes, the darker will be the skin colour Genes do not show additive effect Controlled by many genes Controlled by a few genes Deals with a spectrum of phenotypes , ranging from one extreme to the other Deals with a few clear-cut phenotypes Continuous Variation Discontinuous Variation
  • 6. Artificial selection
  • 7. Artificial selection <ul><li>By crossing different varieties of plants and animals to produce more variations in the offspring </li></ul><ul><li>By selective breeding , special or improved breeds (with desirable traits) of plant and animals are produced </li></ul>
  • 8. Examples of artificial selection
  • 9. Examples of artificial selection
  • 10.  

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