Simple Inheritance in Animals and Plants - B2

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  • Simple Inheritance in Animals and Plants
    • Cell Division and Growth
      • In body cells, chromosomes are found in pairs
      • Body cells need to divide to produce new cells for growth or repair
      • Mitosis produces identical new cells
        • Has a 't' - two pairs of chromosomes - four chromosomes
        • MIT - Making Identical Two
      • Animal cells differentiate early in development but plant cells can differentiate at any time in their life
      • Chromosomes contain genes (alleles) which pass on to each new cell
      • When the cells are unspecialised they are called stem cells
      • In asexual reproduction the cells of offspring are made by mitosis
      • Mitosis Process
        • Normal cell with two pairs of chromosomes (four chromosomes)
          • A copy of each chromosome is made - 4 pairs, 8 chromosomes
            • The cell divides to make it identical to the parent cell - two pairs, four chromosomes
    • Cell Division in Sexual Reproduction
      • Gametes (sex cells) are produced by meiosis
      • Gametes have one set of chromosomes (2 chromosomes)
      • Sexual reproduction gives variation
      • In humans, the gametes are sperm and ova
      • How to remember
      • Process of Meiosis
        • Normal body cell - 2 pairs, 4 chromsomes
          • Chromosomes copy - 4 pairs, 8 chromosomes
            • Cell divides in two - 2 pairs, 4 chromosomes
              • Divide again but separating the pairs so the pairs are different chromosomes - 1 pair, 2 chromosomes
    • Stem Cells
      • Stem cells are not specialised
      • They differentiate into many different types of cell when required
      • They can be used to cure some types of disorders such as paralysis
      • They can be found:
        • in the human embryo
        • in adult bone marrow
    • Mendel and DNA
      • Mendels factors are what we call genes
      • Chromosomes are made o DNA - genes are short sections of DNA
        • Each gene has a particular combination o amino acids to make a specific protein
    • Inheritance in Action
      • Humans have 23 pairs of chromosomes
        • one pair are sex chromosomes
          • females have two X chromosmes
          • Males have one X and one Y
      • Some characteristics are controlled by a single gene
      • Different forms of the same gene are called alleles
        • Some are dominant and some are recesive
      • Genetic Terms
        • Phenotype - physical appearance (dimples, no dimples)
        • genotype - genetic makeup - which allele do they inherit (Dd or dd)
        • Homozygous - both alleles are the same (DD or dd)
        • Heterzygous - both alleles are different (Dd)
    • Inherited Conditions in Humans
      • Some disorders are caused by genes and can be inherited
      • If the allele is dominant the they only need to inherit one dominant allele to get the disorder
        • Eg. polydactyly - extra fingers and toes
      • Cystic fibrosis is caused by a recessive allele and causes the build up of mucus
      • Genetic diagrams are used to predict the chances of offspring inheriting disorders
    • Stem Cells and Embryos - Science and Ethics
      • Embryonic stem cells can be used in medical research and treatments
      • Embryos can be screened for genetic disorders
      • There are economic, social and ethical issues with using embryonic stem cells
      • Ethical - Could be babies, destroyed afterwards, baby can't give permission
      • Economic - Embryonic research is expensive
      • If parents decide to terminate the pregnancy it could be classed as murder


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