Biology Genetics

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  • B1 - Genetics
    • Genetic variation
      • Fertilisation
        • This is when the sperm  and the egg join to form  the full 46 chromosomes.
        • fertilisation is a bit random- you dont know which gametes will join.
      • Mutations (changes) can occur.
        • This just means that there are new characteristics, increasing variation.
      • Gamete formation
        • Gametes are sperm/egg cells. In each pair of chromosomes, one is inherited from the mother and one from the father.
        • Gametes are formed in the ovaries/testes.
        • When these body cells split to form Gametes, chromosomes are split up. Gametes end up with 1/2 the number of chromosomes of a normal body cell - 23.
        • In each gamete, some of your dad's chromosomes are grouped with some of your mums.
        • This shuffling of chromosomes leads to variation in the new generation.
    • Genes and the environment
      • intelligence
        • one theory is that your genes affect your IQ.
          • However, ti may depend on school and upbringing.
      • health
        • Some people are more likely to get diseases(eg cancer) than others.
          • Due to their genes. However, habits such as smoking etc can affect the risk.
      • Sporting ability
        • Genes determine your potentiol, but training ensures you suceed.
    • Sex inheritance and genetic disorders
      • All men have an X and a Y chromosome.
        • Women have two X chromosomes.
        • This is true for all mammals but not plants.
      • Genetic inherited disorders
        • For a child to inherit the disorder, both the parents must be either carriers or sufferers.
          • There is a 1 in 4 chance of the child having the disorder if both parents are carriers.
        • The allele which causes cystic fibrosis is a recessive allele, carried by 1 in 25 people.
          • as it is recessive, people only carrying one copy of the allele wont have the disorder.
            • Theyre known as carriers.
    • Genes and chromosomes
      • In most animal cells chromosomes come in pairs
        • humans have 23 pairs of chromosomes where as guinea pigs have 32.
      • Chromosomes carry genes. Genes control development of different characteristics.
        • eg. eye colour
      • Most cells in your body has a nucleus.
        • The nucleus contains genetic material in the form of chromosomes
      • genes are short lengths of a chromosome - which is a long length of DNA.
      • DNA is coiled up to form the arms of the chromosome


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