. Die Vererbung ist. Zytogenetik. 362 ZELLE VERERBUNG braunes Pigment cd + 3-OH-Kynurenme Kynurenme 1 Formylkynurenine,. w + Tryptophan Abbildung 12.4. Die biochemische Grundlage der genetischen Kontrolle von Augenfarbe bei Drosophila (von Wagner und Mitchell, 1955, Genetik und Mefabolism, New York, Wiley; nach Beadle, 1945, Chem. Rev., 37: 15). Diese und andere Stoffe, die in Sequenz als Vorläufer der braunes Pigment im Insekt Auge (Abbildung 12.4). Die Reparable versus irreparablen Charakter der lethals hat auch prüfverfah-gated in Drosophila mit der Verwendung somatischer Überquerung mit der gleichen y und

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. Cell heredity. Cytogenetics. 362 CELL HEREDITY Brown pigment cd + 3-OH-Kynurenme Kynurenme 1 Formylkynurenine I, . w+ Tryptophane FIGURE 12.4. The biochemical basis of the genetic control of eye color in Drosophila (from Wagner and Mitchell, 1955, Genetics and Mefabolism, New York, Wiley; after Beadle, 1945, Chem. Rev., 37:15). established this and other substances in sequence as precursors of the brown pigment in the insect eye (Figure 12.4). The reparable versus irreparable nature of lethals has also been investi- gated in Drosophila with the use of somatic crossing over with the same y and sn genes shown in Figure 12.2. If, for example, there were a lethal gene adjacent to the yellow marker on the upper chromosome, and if twin spots regularly occurred, it would be concluded that the lethal does not prevent the survival of a patch of cells homozygous for it as long as the rest of the animal remains heterozygous. On the other hand, if single singed spots were of regular occurrence, we would know they were the survivors of segregations that would have led to twin spots ex- cept that the yellow-lethal homozygote did not survive. Demerec found with the use of this method that there are both kinds of sex-linked lethals. Most lethals that are demonstrated to be deficiencies are also autonomous and are cell lethals, but those that survive when present on the single X of the male make for viable cells. Some deficiences are so restricted in scope as to not include an irreparable functional unit that even haploid "organisms " such as phages survive their presence. Somatic crossing over is not restricted to the X chromosome of Dro- sophila. It occurs between other chromosomes and in other organisms, such as yeast and fungi. An extensive analysis of the process has been carried out by Pontecorvo and his associates in Glasgow with the fungus, Aspergillus nidulans, where the products of somatic crossing over can be recovered and analyzed. This organism contains haplo

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• bookcentury1900
• bookcollectionbiodiv
• bookpublishernewyorkwiley