biology aqa gcse - inheritance,variation and evolution

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  • inheritance, variation and evolution
    • DNA
      • DNA - deoxyribonucl-eic acid. its a chemical that all genetic material is made up of.
      • your DNA  decides what genetics you inherit, your characteristic
      • chromosomesnormally come in pairs. every human being has 23 pairs of chromosomes
      • DNA is a polymer, its made up of two strands coiled together in the shape of a double helix
      • only 20 amino acids are used, genes tell cells what order to put amino acids together
      • a gene is a small section of DNA found on a chromosome, each gene codes for a particular sequence.
    • Reproduction
      • the mother and father produce gametes
      • sexual reproduction is where genetic information from two organisms is combined to produce offspring which is genetically different to either parent
      • asexual reproduction produces genetically identical cells
        • there's only one parent, so the offspring are genetically identical to that parent
        • asexual reproduction happens by mitosis - an ordinary cell makes a new cell by dividing in two
        • the new cell has the same genetic information - this is called a clone
      • meiosis
        • before the cell begins to divide, it duplicates its genetic information.
        • in the first division the chromosome pairs line up in the centre of the cell
        • the pairs are then pulled apart so each new cell has only one copy of each chromosome
        • in the second division, chromosomes line up in the centre of the cell and the arms are pulled apart
        • you end up with four gametes each with only a single set of chromosomes in it.
    • Genetics
      • to transfer a gene responsible for a desirable characteristic form one organisms genome into another organism
      • bacteria has been modified to to produce human insulin to treat diabetes
      • there are worries about the long term effects of modifying genetics
      • fossils
        • three ways fossils form in rocks:
          • form in rocks from gradual replacement by minerals
          • form in rocks from casts and impressions
          • form in rocks from preservation
        • fossils are remains of plants and animals
      • classification
        • K - Kingdom      P - Phylum    C - Class         O - Order       F - Family      G - Genus       S - Species
          • or
          • clean
          • frogs
          • ponds
          • sick
          • get
          • keep
        • every organism is given its own two - part Latin name so that scientists all over the world can understand and don't need to translate
          • ie. humans were given the name Homo sapien
    • evolution
      • Charles Darwin's theory of evolution - evolution by natural selection
      • natural selection - the process in which evolution takes place. organisms produce more offspring than the land can manage, only those that adapt to the land can survive and produce their own offspring
      • theory of evolution - all of today's species have evolved from simple life forms that started to develop over 3 billion years ago.
      • survival of the fittest
      • selective breeding
        • organisms are selectively bred to develop features that are useful or attractive
          • animals that produce meat or milk
          • crops with disease resistance
          • dogs with a good, gentle temperament
          • decorative plants with big or unusual flowers
        • take the best plants or animals and breed them together to get the best possible offspring


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