A comparison of the ultraviolet absorption of haploid and diploid salivary gland chromosomes

1. 1. Measurements of the total amount of ultraviolet (chiefly 257 and 275 mμ) absorbing material in the salivary gland chromosomes of triploid Drosophila melanogaster have been made, using the photographic method for microspectrophotometry. 2. 2. The total extinction of a paired diploid chromosome in a triploid nucleus is found to be twice that of the haploid homolog with which it has failed to pair. The deviations in measurements of parts of sixteen pairs of chromosomes in seven nuclei were found to be within the errors of the method. 3. 3. Deviations were random with respect to the relative thickness of the diploid and haploid homologs. Lambert's law is, therefore, applicable to this material over a range of thicknesses of at least two to one. 4. 4. The state of being paired is shown not to have an effect on the amount of material in fully grown salivary gland chomosomes.