Medical genetics / edited by Victor A. McKusick and Robert Claiborne.

Date:
[1973]
Catalogue details

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

Credit: Medical genetics / edited by Victor A. McKusick and Robert Claiborne. Source: Wellcome Collection.

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    CHROMOSOME IDENTIFICATION BY FLUORESCENCE By previous techniques it was possible to classify chromosomes into groups of different length but not always to separate mem¬ bers of a group by morphologic or autoradiographic analysis. This was especially true of the С group, which includes the X and numbers 6 through 12. As can be seen above, such individual separation can now be accomplished by fluorescence, both by visual inspection of the QM bands and, even mare effectively, from the associated fluorometric curves (Hereditas 67:97, 1971). By moving the stage, the slit can in effect be moved along the entire length of the chromosome; by means of a beam-splitter, part of the light is passed into an eyepiece within which is marked the orientation of the slit, so that the operator can adjust the photograph for proper scanning. The remainder of the light is passed into a photomultiplier and amplifier, producing an electric current that con¬ trols the Y-input of an ordinary XY recorder, the X-input being controlled by the motion of the stage. In certain cases — e.g., if the chro¬ mosome varies considerably in width - we use a circular diaphragm with an equivalent diameter of 0.2 fim, which is moved along the length of a single chromatid. The result in either case is a curve showing the variations in light intensity along the entire length of the chromosome or chro¬ matid. If desired, the machine can also be hooked up to a digitizer and tape- puncher, producing a series of numeri¬ cal values that can be fed directly into a computer. Extensive studies of these curves, based on more than 30,000 examples, show that they are highly repro¬ ducible and consistent. As one would expect from what was said earlier about the fluorescence patterns them¬ selves, there are variations in the curve of a given chromosome from one individual to another and often between two paired chromosomes of one individual, but despite these varia¬ tions the curves for a particular chro¬ mosome are all clearly more like one another than like any other curve. Moreover, the curves possess enough detail to permit characterization of regions within chromoson\es. Before saying more about the curves and what they can be used for, we should say a word about some other staining techniques that are now coming into use for chromosome identification. There are a consider¬ ai