• D. J. Nolte

      Articles written in Journal of Genetics

    • The eye-pigmentary system ofDrosophila: The pigment cells

      D. J. Nolte

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    • The eye-pigmentary system ofDrosophila - II. Phenotypic effects of gene combinations

      D. J. Nolte

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    • The eye-pigmentary system ofDrosophila - III. The action of eye-colour genes

      D. J. Nolte

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      This investigation was mainly directed at the solution of the problem of the multiplicity of eye-colour genes inDrosophila melanogaster.

      For the purposes of routine quantitative comparison of the red and brown eye pigments of different mutant strains with those of the wild-type, methods are described for the rearing of normal-sized flies and for the extraction of the two pigments and their spectrophotometric analysis. The light-absorption curves are given of these pigments in the wild-type and various mutants, singly and in combination. The two pigments typical of the wild-type are found in all mutants with the exception of the alleles of the white locus which condition the production of a qualitatively changed red pigment.

      Quantitative estimations of the pigments in the wild-type and the different mutants studied indicate the following effects of mutant genes:wm4 has decreased amounts of both pigments, with the red pigment content varying greatly with temperature changes;ras2 has a decreased amount of red pigment; the genes of the ruby group,rb, cm, g3 andcar, effect a reduction in the content of both pigments, but there is no simple relation between the amounts of this reduction, the four genes showing differential effects on the two pigments; the alleles ofw reduce the amount of red pigment to a great extent and the brown pigment content to a varying extent for the different alleles, but again the effects on the two pigments are differential, there being no simple linear quantitative ratio between the amounts in the different alleles;st suppresses the production of the brown pigment but possibly causes an increase in red pigment content;bw suppresses the production of the red pigment (unless a small amount of qualitatively changed red pigment is formed) and also reduces the brown pigment content; combinations between the genes of the ruby group,inter se and withst andbw, show sub-additive interaction effects and an overlapping in the mode of their action; two alleles ofcar show a simple quantitative relation in the amount of red pigment produced.

      A scheme is presented to show some of the interrelationships which exist between the various genes which affect eye pigmentation. The probable mode of action of the normal allele of white is at the level where a common substrate is differentiated for the formation of specific substrates for the red and brown chromogens, but where also certain by-products are formed for utilization in the protein carrier and granule system. The normal alleles of scarlet and brown then fit into the scheme at a later level, i.e. that of chromophore or chromoprotein formation. The action of the normal allele of raspberry2 seems to be at the level of cellular differentiation. In connexion with the mode of action of the normal alleles of the genes for ruby, carmine, garnet3 and carnation the concept is developed that many eye-colour genes affect eye pigmentation only indirectly, i.e. eye colour is influenced by them epigenetically, consequent on their main function being the directing of enzyme specificities for the breakdown and resynthesis of proteins during metamorphosis; the products of breakdown are utilized in the eye-pigmentary system which in this activity is partly an excretory system.

    • The eye-pigmentary system ofdrosophila - IV. the pigments of the vermilion group oe mutants

      D. J. Nolte

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      The large number of eye-colour mutants ofDrosophila melanogaster is classified into several groups: vermilion, light, dark, ruby, red and variegated. The first group studied histologically and photometrically was the vermilion group, with the mutants scarlet (st), cinnabar (cn), vermilion(v), cardinal(cd) and karmoisin(kar).

      Histologically the eyes of these mutants are very similar excepting that inst largersized granules (or aggregates) occur amongst the normal granules in the secondary pigment cells, and incd a smaller number of such granules appear in the distal parts of these cells.

      The validity of the method of differential double extraction of the red and brown pigments is examined.

      Evidence, based on the spectrophotometric curves of the extracts, is advanced for the affinities of the red and brown pigments, a common step in their chromophore formation being postulated during the stage of development of a precursor, or constituent, for combination with their specific chromogens.

      An analysis of the light-absorption curves of pupal and imaginal eye extracts gives some indication of the course of development of the red and brown chromophores.

      The five mutants produce mainly red pigment, although in the case ofcd a small amount of brown pigment is also produced and inkar about twice this amount. In regard to the red pigment content in these mutants no great difference was found as compared with the wild-type, excepting in the case ofcd which proved to possess a significantly greater amount.

      To the known functions of the normal alleles ofv andcn may now be added some assumptions on the probable roles of the normal alleles ofst, kar andcd, these genes probably conditioning stages in the preparation of the substrate provided by the normal allele of white for combination with the brown chromogen, to result in the production of the brown chromophore.

    • The eye-pigmentary system ofdrosophila - V. the pigments of the light and dark groups of mutants

      D. J. Nolte

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      The second and third groups of eye-colour mutants ofDrosophila melanogaster, studied histologically and photometrically, are the light group with the mutants light (lt), lightoid(ltd) and persimmon(pers), and the dark group with the mutants sepia(se), clot (cl), Henna-recessive (Hnr) and Plum2 (Pm2).

      Inlt andpers a small percentage of granules is larger than normal and the type of pigmentation histologically is a light brownish; inltd the general colour is reddish brown, most granules are much larger than normal but less in number, and while the primary and basal pigment cells are not clearly delineated by their pigment granules, a clumping of granules occurs in the proximal parts of the secondary pigment cells. Incl and Hnr the histological picture is like that of the wild-type, while inse andPm2 it resembles the brown mutant type in general colour.

      In all the mutants, excepting two, the normal types of red and brown pigments occur. Inse a modified red pigment is found, with a greenish yellow colour in solution and a changed spectrophotometric curve with a peak of absorption at 415 mµ instead of 480 mµ; incl a mixture of this modified pigment and the normal red pigment occurs.

      Inltd, lt andpers a great reduction in the amounts of both pigments as compared with the wild-type was determined; inPm2 the brown pigment content is equivalent to that of the mutant brown, but the red pigment content is appreciably higher; inHnr,se andcl the content of red pigment, or its modified form, shows a reduction as compared with the wild-type, but the amount of brown pigment is significantly higher. It is calculated that the eyes ofcl contain about 36% of the red pigment found in the wild-type and 84% of the yellow pigment found in sepia.

      An attempt is made to indicate the possible modes of action of these genes in eye pigmentation. It is postulated that the normal alleles oflt andpers, like those of the ruby and carnation mutants, are eye-colour genes indirectly only, their main function being the directing of enzyme specificities, especially for the breakdown of proteins during metamorphosis, some of the breakdown residues being utilized in the pigmentary process; the normal allele ofltd seems to play some part during pigment granule production. The action ofPm2 seems to be clue to a position effect of thebw+ locus, its prohibitive effect on red pigment production being less efficient than that of the mutant brown. The normal alleles of Hnr,se andcl seem to fit into the reaction chain for the production of a common basic precursor or constituent which is later differentiated by thew+ gene into specific substrates for the formation of the red and brown chromophore groups. Hnr seems to divert some of this constituent from the red pigment to the brown pigment pathway, whilese andcl seem seem to stand in a sequential relation to each other, their action (in the case of the latter only partly) being to modify the basic precursor in such a way that a modified red pigment results, and in addition a part of this substance destined for the red pigment substrate is diverted to the brown pigment production chain.

    • The eye-pigmentary system ofDrosophila - VI. The pigments of the ruby and red groups of mutants

      D. J. Nolte

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      The fourth and fifth groups of eye-colour mutants ofDrosophila melanogaster studied histologically and photometrically, are the ruby group with the mutants purple (pr), rosy (ry), pink (p), purpleoicl (pd), claret (ca), maroon (na) and prune (pn), and the red group with the mutants safranin2 (sf2), sepiaoid (sed), dark eye (dke), mahogany (mah), bordeaux (bo) and Moiré ().

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