DNA and cell division

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  • Created by: emews
  • Created on: 14-11-17 17:55
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  • DNA and cell division
    • DNA molecules are large and complex. They carry the genetic code that determines the characteristics of a living organism.
    • Except for identical twins, each person’s DNA is unique. This is why people can be identified using DNA fingerprinting.
      • DNA can be cut up and separated, forming a sort of 'bar code' that is different from one person to the next.
    • A gene is a section of DNA that codes for a specific protein.
    • The cell’s nucleus contains chromosomes. These are long threads of DNA, each made up of many genes.
    • There are four different bases in DNA:
      • thymine, T
      • adenine, A
      • guanine, G
      • cytosine, C
      • They always pair up in a particular way, called complementary base pairing:
        • thymine pairs with adenine (T–A)
        • guanine pairs with cytosine (G–C)
    • The chromosomes in a pair carry the same genes in the same places. But there are different versions of the same gene.
      • Different versions of the same gene are called alleles.
    • In mammals, body cells are diploid. The chromosomesneed to be copied exactly so that new cells can be produced for:
      • growth
      • repair to damaged tissue
      • replacement of worn-out cells
      • Mitosis produces two genetically identical cells in which the number of chromosomes is the same as in the original cell.
    • Meiosis is the type of cell division that produces gametes.
      • Meiosis produces four genetically different haploid cells. Unlike mitosis, meiosis is a reduction division – the chromosome number is halved from diploid (46 chromosomes in 23 pairs in humans) to haploid (23 chromosomes in humans).

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