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Crossing over and independent assortment

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Crossing over and independent assortment

  1. 1. Independent assortmentandCrossing over<br />Year 12 Biology<br />Grant McKenzie<br />
  2. 2. Meiosis<br />Meiosis in not just about reducing the number of chromosomes to half that found in somatic cells<br />Going from diploid to haploid<br />It is much more important<br />
  3. 3. Chromosomes<br />Each homologous chromosome has alternative forms of a gene<br />Called alleles<br />One allele comes from mother, the other from the father<br />The alleles are responsible for dominant and recessive traits<br />
  4. 4. Meiosis promotes<br />Used to ensure that hereditary variability is maintained in a species<br />Lies at the core of evolutionary change<br />Without this change<br />Organisms would not adapt to a changing environment<br />
  5. 5. Processes that promote Variation<br />Independent Assortment<br />Is the random assortment of paternal and maternal chromosomes in gametes<br />Each sperm or egg mixture of chromosome originating from mum or dad<br />
  6. 6. Draw Picture of Independent assortment<br />
  7. 7. The math of Independent Assortment<br />Father<br />Abc<br />Mother<br />aBC<br />The child will be<br />AabBcC<br />The child will be<br />AabBcC<br />23<br />Gametes produced by child<br />Abc<br />ABc<br />AbC<br />ABC<br />Abc<br />aBc<br />aBC<br />abC<br />
  8. 8. The math of Independent Assortment<br />The maths becomes more complicated with more chromosomes<br />Can yield 223 unique was to arrange the 23 pairs of chromosome<br />8,388,608 possible ways<br />This feature alone would lead to high levels of variation<br />
  9. 9. Looking at Independent Assortment<br />We will look at Independent assortment<br />Dihybrid Inheritance<br />
  10. 10. Crossing Over<br />Also called recombination<br />Makes the number of possibilities even greater<br />Paternal and Maternal chromatids exchange corresponding genetic material<br />Paternal and maternal refer to the origin of the chromosomes<br />
  11. 11.
  12. 12. Explore with Crossing over with Modelling clay<br />Use modelling clay to explore crossing over<br />Make 2 chromosomes<br />Use different colours for the different chromosomes<br />Explore single cross overs<br />Explore double cross overs<br />Always keep in your mind about alleles and the order of the genes along the length of the chromosome<br />
  13. 13. Recombination<br />There is no loss of gain of genetic material during recombination<br />Just an equal exchange of genetic material <br />
  14. 14. Segregation<br />During Meiosis<br />Alleles of different genes on different chromosomes segregate<br />Segregation occurs independently of each other<br />Individual is heterozygous at two genes<br />AaBb<br />The segregation of the A allele is different from the a allele is independent of the segregation of the B and b alleles<br />There will be an equal number of AB, Ab, aB and ab gametes formed<br />

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