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Variation

Variation . Why are we all so different??. What is Variation?. Variation means different. We are all different due to the special sequence of bases along our DNA, - they are unique in every person. If you change the recipe, you change the cake. Why is variation important?.

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Variation

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  1. Variation Why are we all so different??

  2. What is Variation? • Variation means different. We are all different due to the special sequence of bases along our DNA, - they are unique in every person. If you change the recipe, you change the cake.

  3. Why is variation important? • It is vital that variation exists within a population because in times of environmental stress or change, some organisms will be better adapted to survive, so some of the species will continue. Eg if after a fire, trees would be black and sooty. Which bug would survive the best? Why?

  4. How do we get variation? • Variation (changes in the base sequence for a gene or genes) can be created by 3 main methods: • 1. Meiosis and sexual reproduction • 2. Mutations • 3. Environmental conditions

  5. 1. Sexual reproduction • When an organism reproduces sexually, there are two parents and their gametes (sex cells) are combined to create a new individual. The gametes are created by MEIOSIS.

  6. In Meiosis – crossing over occurs to mix up genes In Meiosis, once the chromosomes have replicated, they line up next to each other. When this happens, some parts can get swapped. This is called crossing over.

  7. Independent/random assortment of chromosomes into the gamete • Once the chromosomes have been copied and crossed over, it is purely chance, which combinations of the chromosomes end up in one gamete (sex cell) together. You can end up with more maternal or paternal copies, or a mixture of both. This is called random assortment – which is like a lucky dip!

  8. Random fusion of gametes/random fertilisation. • When sperm (or pollen) and egg (ova) have been created, it is purely CHANCE which of the many sperm (or pollen) fuse/join with which egg. This is called random fusion of gametes. Together, they form a zygotewhich contains a full set of chromosomes ie 23 Pairs, one of each pair from mum, one from dad. 

  9. Summary:

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