DNA and chromosomes

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  • Created by: Laura
  • Created on: 17-04-14 10:32
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  • DNA and Chromosomes
    • In prokaryotic cells, such as bacteria, the DNA molecules are smaller, form a circle and are not associated with proteins. They do not have chromosomes.
    • Eukaryotic cells, the DNA molecules are large, form a line rather than a circle and occur in associations with protein structures called chromosomes.
    • Chromosome structure
      • Chromosomes only visible when cell is dividing.
      • When visible they appear as two threads, joined at a distinct point. Each thread is called a chromatid
      • The DNA in chromosomes is held in place by proteins
      • DNA is coiled into a double helix and the double helix is wound around the proteins to keep it in place... this forms the chromosome
    • Homologous chromosomes
      • Each offspring gets half the chromosomes from their mum and half from their dad. These match up to form homologous pairs
      • A homologous pair is always two chromosomes that determine the same genetic characteristic but arent exactly identical
    • What is an allele?
      • Each gene occurs in two, occasionally more, different forms. Each of these forms is called an allele.
      • Each individual inherits one allele from each parent. They may be the same of they may be different
      • When they are different each allele will code for a different polypeptide
      • The alleles individuals inherit may not always code for something that is necessary for them to live such as a specific enzyme.


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