Chromosomes

• Chromosomes carry the genetic information of a cell
• A chromosome is made up of a mass of coiled threads of DNA and proteins
• In a cell that is not actively dividing, the chromosomes are translucent to both light and electrons. When the cell starts to actively divide, the chromosomes condense - they become shorter and denser and will absorb stains very readily
• Histones are positively charged proteins involved in the coiling of DNA to form dense chromosomes in cell division. The DNA winds around the histones to form dense clusters known as nucleosomes. These interact to produce more coiling and then supercoiling to form dense chromosome structures visible through a microscope in the nucleus of a dividing cell. In the supercoiled areas, the genes are not available to be transcribed to make proteins
• The cells of each species posses a characteristic number of chromosomes - human have 46 chromosomes. These chromosomes occur in matching pairs, one of each pairs originate from each parent.
• Before a cell divides, it must duplicate the original set of chromosomes. During mitosis, these chromosomes are equally divided between the two new cells so that each have a complete and identical set of genetic information.
• During the active phases of cell division, the chromosomes become very coiled and condensed. In this stage they can be photographed to produce a karytope
• 1. Telomere
  2. Short arm
  3. Centromere
  4. Longer arm
  5. Sister chromatids