Working with animal chromosomes / Herbert C. Macgregor and Jennifer M. Varley ; chapter 7 contributed by Aimee Bakken, R. Stephen Hill.

  • Macgregor, Herbert C.
Date:
[1983], ©1983
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Working with animal chromosomes / Herbert C. Macgregor and Jennifer M. Varley ; chapter 7 contributed by Aimee Bakken, R. Stephen Hill. Source: Wellcome Collection.

    125/280 (page 105)
    Polytene chromosomes 105 B. А quick method for Chironomus A simplified technique can be employed to make temporary preparations suitable for examination in a laboratory practical class. Equipment required for this technique is minimal and is outlined below: (a) Dissecting microscope (b) Ordinary but very clean microscope slides and coverglasses (c) Forceps or dissecting needles (d) 45% acetic acid (e) Acetic-orcein (0.5% orcein in 45% acetic acid) (f) Filter papers (g) Microscope with bright field optics (h) Nail varnish or rubber cement The basic method of preparation is identical to the one just outlined, but instead of using forceps to decapitate the larva, dissecting needles can be used. The dissecting needles should be laid across the body and behind the mouthparts, the larva should not be speared with them. If phase contrast optics are not available, the glands should be fixed in acetic-orcein as de¬ scribed previously, and the squashing monitored using bright field optics. Subbed slides and siliconized coverglasses are only necessary for permanent preparations, if anything squashing will be slightly easier if ordinary slides are substituted. After squashing, the preparation can be sealed by applying nail varnish or rubber cement around the edge of the coverglass to prevent drying out. If the polytenes are to be examined using high power objectives, be careful that the objectives do not touch wet nail varnish! Remember that although subbed slides and siliconized coverglasses are not necessary for temporary preparations, it is still essential that the slides and coverglasses are thoroughly clean and dust free. C. Polytene chromosomes by Nomarski microscopy Structures in the polytene nucleus such as the nucleolus and the Balbiani rings may not be readily apparent in preparations which have been fixed, stained, or dehydrated. One way of visualizing such features easily is by direct examination of the polytene cell by using phase contrast or Nomarski interference microscopy. The technique for direct examination is identical to that for making per¬ manent preparation as far as, and including, the actual squashing procedure. Once the tissue has been squashed sufficiently, seal the edge of the coverglass with nail varnish or wax and examine using phase contrast optics.