Reproduction and Inheritance. 

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  • Reproduction and Inheritance in humans.
    • Human body cells are diploid - they have two copies of each chromosome, arranged in pairs.
    • Genes are chemical instructions.
      • proteins control inherited characteristics.
        • genes also control our inherited characteristics.
          • There can be different versions of the same gene, which give different versions of a characteristic.
            • These different versions are called alleles.
    • A DNA molecule has two strands coiled together in the shape of a double helix.
      • There are four different bases: adenine, cytosine, guanine and thymine.
        • The bases are always paired up in the same way, A-T C-G, this is called complementary base-pairing.
    • Asexual reproduction involves only one parent. The offsring have identical genes to the parent.
      • Mitosis: DNA is spread out into long strings. DNA duplicates so theres one copy for each new cell. DNA forms X shaped chromosones
        • Chromosomes then line up at centre of cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
          • Membranes form around each of the new sets of chromosomes. Nuceli of tow new cells.
            • cytoplasm divides.
    • Sexual reproduction involves the fusion of male and female gametes. Because their are two parents, the offspring contain a mixture of their parents gene.
      • Meiosis: cell duplicates it DNA (so theres enough for each new cell). In first division chromosomes line up in pairs in the centre of the new cell.
        • The pairs are then pulled apart so each new cell only has one copy of each chromosome. each cell will have mixture of Mothers and Farthers creating variation.
          • In 2nd diivision chromosomes line up at centre of cell and arms are puller apart.
            • You get four haploid gametes, eahc cell only have single set of chromosomes, the gametes are genetically different.


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