variation and genetic variation

  • Created by: tia5sos
  • Created on: 22-11-20 14:40
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  • variation and genetic variants
    • variation can be continuous or discontinuous
      • continuous variation is when the individuals in a population vary within a range - there are no distinct categories, e.g. humans can be any height within a range, not just tall or short.
        • other examples include an organism's mass, and the number of leaves on a tree.
          • characteristics that are influenced by more than one gene or that are influenced by both genetic and environmental factors usually show continuous variation.
      • discontinuous variation is when here are two or more distinct categories- each individual falls into only one of these categories, there are no intermediates.
        • for example, humans can only be blood group A, B, AB or O.
          • characteristics that are only influenced by one gene and that aren't influenced by the environment are likely to show discontinuous variation.
    • mutations are changes to the genome
      • 1. Occasionally a gene may mutate. A mutation is a rare, random change in an organism's DNA that can be inherited.
      • 2. Mutations mean that the sequence of DNA bases in the gene is changed, which produces a genetic variant (a different form of the gene).
      • 3. As the sequence of DNA bases in a gene codes for the sequence of amino acids that a make up a protein, gene mutations sometimes lead to changes in the protein that it codes for.
      • 4. Most genetic variants have very little or no effect on the protein that the gene codes for. Some will change it to such a small extent that its function is unaffected. This means that most mutations have no affect on an organism's phenotype.
      • 5. Some variants have a small influence on the organism's phenotype - they later the individuals characteristics but only slightly.
        • for example, some characteristics, e.g. eye colour, are controlled by more than one gene. A mutation in one of the genes may change the eye colour a bit, but the difference might not be huge.
      • 6. very occasionally, variants can have such a dramatic affect that they determine the phenotype.
        • For example, the genetic disorder, cystic fibrosis, can be caused by the deletion of just three bases but it has a huge affect on phenotype.
          • The gene codes for a protein that controls the movement of salt and water into and out of the cells.
            • However, the protein produced by the mutated gene doesn't work properly.
              • this leads to excess mucus production in the lungs and digestive system, which can make it difficult to breathe and to digest food.


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