Human afflictions and chromosomal aberrations / Raymond Turpin and Jérôme Lejeune.

  • Turpin, Raymond, 1895-1988
Date:
1969
Catalogue details

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

Credit: Human afflictions and chromosomal aberrations / Raymond Turpin and Jérôme Lejeune. Source: Wellcome Collection.

    60/412 (page 44)
    44 HUMAN AFFLICTIONS AND CHROMOSOMAL ABERRATIONS outset that these two chromosome pairs are extremely similar. A mathematical analysis of the density of points per unit area may be considered; however, in view of the difficulties of this type of analysis we prefer to use a very simple optical procedure. A photographic negative of the point scatter is projected onto sensitive paper taking care to open the objective as far as possible and to bring the enlarger well out of focus. Under these conditions a point is no longer represented by its image but by a diffraction spot centred on the theoretical site of the point and the diameter of which depends solely on the numerical opening of the objective and the extent of defocusing. A defect of this technique is that it yields a diffraction pattern of more or less uniform intensity whereas the ideal representation of the probable site of a point should be an image with diminished intensity at the edges (Gaussian distribution). Despite this imperfection the technique of the blurred image has the advantage of giving overlapping images of adjacent points and of summing the quantities of light corresponding to the diffraction spots. In the case of group 4-5, Fig. 3.6 shows that despite a fairly erratic distribution of the spots, two distinctly marked condensation centres are discernible, one situated at the coordinates L = 63 0 and Ic = 26-5, the other at the coordinates L = 59-8 and Ic = 28-4. It is thus reasonable to assume that the first point corresponding to the longest chromosome must be considered as the site of chromosome 4, the other point corresponding to the site of chromosome 5 (Fig. 3.7). It is quite difficult to define the statistical significance of this topographical correlation but it is at least interesting to compare these results with the statistical calculation previously made by the pairing-off method. The agreement between the two methods is satisfactory within the limits of the imperfections of the technique but the method of blurring has the advantage of bringing out a distinctive difference between the two chromosomes, 4 is longer than 5 (by definition) but also its centromere is a little more distal than that of 5. Although these are slight differences, this simple observation makes it possible in good quality preparations to make the pairing-off method much more precise. Group 6-12 and X Measurement of the chromosomes of this group and plotting each of them on the graph gives the image in Fig. 3.8. The optical arrangement previously indicated reveals the existence of quite