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Inheritance, Variation and Evolution (Reproduction (Asexual reproduction…

- - - - 20 amino acids are used in the making of a specific protein.
  - - - Allows scientists to identify genes in the genome that are linked to different types of disease.
      - Knowing which genes are linked to inherited diseases could help to understand them better and could help to develop effective treatments.
      - Scientists can look at genomes to trace the migration of certain populations of people around the world.
- - - - Each nucleotide consists of one sugar molecule, one phosphate molecule and one 'base'.
    - - A always links up with T, and C always pairs up with G. This is called complementary base pairing.
        
        It's the order of bases in a gene that decides the order of amino acids in a protein.
  - - - To make proteins, ribosomes use the code in the DNA.
        
        The process by which the code gets from the DNA to the ribosome is done using a molecule called mRNA.
        
        mRNA is made by copying the code from DNA and mRNA acts as a messenger between the DNA and the ribosome - it carries the code between the two.
- - - - Insertions are where a new base is inserted into the DNA base sequence where it shouldn't be.
      - Every three bases in a DNA base sequence codes for a particular amino acid.
      - An insertion changes the way the groups of three bases are 'read', which can change the amino acids that they code for.
    - - Deletions are when a random base is deleted from the DNA base sequence.
      - Deletions change the way that the base sequence is 'read' and have knock-on effects further down the sequence.
    - - Substitution mutations are when a random base in the DNA base sequence is changed to a different base.
- - - - Sexual reproduction involves the fusion of male and female gametes. Because there are two parents, the offspring contain a mixture of their parents' genes.
        
        This mixture of genetic information produces variation in the offspring.
    - - In humans, each gamete contains 23 chromosomes which is half the number of chromosomes in a normal cell.
        
        The egg and sperm fuse together (fertilisation) to form a cell with the full number of chromosomes (half from mother, half from father).
  - - - The offspring are genetically identical to the parent (clones).
    - - The new cell has exactly the same genetic information as the parent cell.
  - - - This means they are more likely to breed successfully and pass the genes for the characteristics on. This is known as natural selection.
  - - - This means that asexual reproduction uses less energy than sexual reproduction, because organisms don't have to find a mate.
      - This also means that asexual reproduction is faster than sexual.
  - - - Spores can be produced sexually and asexually.
        
        Asexually-produced spores form fungi that are genetically identical to the parent fungus.
        
        Sexually-produced spores introduce variation and are often produced in response to an unfavourable change in the environment, increasing the chance that the population will survive the change.
  - - - For example, plants that grow from bulbs (e.g. daffodils). New bulbs can form from the main bulb and divide off. Each new bulb can grow into a new identical plant.
- - - - This process involves two cell divisions. In humans, it only happens in the reproductive organs (in females it's the ovaries and in males, the testes.