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  1. 1. Alleles Bradley has two alleles for ginger hair
  2. 2. Objectives <ul><li>different types of a gene controlling the same characteristic are called alleles . </li></ul><ul><li>some alleles always work ( dominant ones). </li></ul><ul><li>some alleles only work if there are two copies (i.e. no dominant allele present). These are called recessive . </li></ul>
  3. 3. Eye colour <ul><li>We get an allele for eye colour from each parent </li></ul><ul><li>We shall call these alleles B for brown and b for blue </li></ul><ul><li>B is dominant </li></ul><ul><li>b is recessive </li></ul>
  4. 4. Genotype <ul><li>The alleles you have could be: </li></ul><ul><li>BB = brown </li></ul><ul><li>Bb = brown </li></ul><ul><li>bb = blue </li></ul><ul><li>These letters are called your genotype </li></ul>
  5. 5. How do you inherit eye colour? <ul><li>If you have brown eyes, then at least one parent must have brown eyes </li></ul><ul><li>If you have blue eyes, both or one or none of your parents could have blue eyes </li></ul>
  6. 6. How does this work? <ul><li>To have brown eyes, you only need one copy of the brown allele B </li></ul><ul><li>You could get this from either parent </li></ul>
  7. 7. How does this work 2? <ul><li>To have blue eyes you need 2 copies of the blue allele b </li></ul><ul><li>You must get one from each parent </li></ul><ul><li>If these parents also have B alleles then they will have brown eyes (they are ‘carriers’ for blue eyes) </li></ul>
  8. 8. Does anything else work this way? <ul><li>Yes, hair colour (like Bradley’s) and some diseases (eg cystic fibrosis) are inherited in a similar way </li></ul>
  9. 9. Punnet square B b b B
  10. 10. Plenary <ul><li>Scientists believe that ginger hair will one day disappear. Why is this? </li></ul><ul><li>Harder – why has ginger hair survived for so long? </li></ul><ul><li>All about alleles sheet </li></ul>