The Principles of Clinical Cytogenetics - Extra Materials - Springer

82 Christopher McAleer
Fig. 1. Schematic diagram of a brightfield microscope illustrating the basic components. (Reprinted with
permission of Olympus America, Inc.)
the wavelength used for viewing. For this reason, shorter wavelengths of light (green–blue) have
greater resolving capabilities than longer ones (yellow–red).
Resolving power is also influenced by the color and brightness difference (contrast) between
two objects, as well as the contrast of the background on which the objects appear. When an image
has a low range of contrast, it is more difficult for the eye to detect structures resolved by the
microscope components. Stains used for G-banding act to increase the contrast range of a chromosome
by absorbing transmitted light in areas where the stain has bound. This produces bands of
varying intensity, as regions with more stain allow less light to be detected. Green light enhances
this absorption effect, as G-banding stains strongly absorb green wavelengths. This increases the
overall contrast range of the image, allowing the eye to detect more of the subtle details of chromosome
morphology and banding. For these reasons, a green filter is recommended for routine chromosome
analysis.