. Biological order. Biology. BIOLOGICAL ORDER repressor is present. In the zygote type II, the female cytoplasm is i~. This corresponds to constitutivity. No repressor is present, and the enzyme is synthesized, thanks to the gene z+ introduced by the male. But the male has introduced at the same time the phase I • :/?-galactosidase X = repressor • X •. HOURS Figure 19. Synthesis of /3-Galactosidase by a Heterozygote. The heterozygote of type II shown in the preceding figure has been formed by the transfer of the male genes i+ z+ into the i~ z~ female. The female, being constitutive (i~), is de
. Biological order. Biology. BIOLOGICAL ORDER repressor is present. In the zygote type II, the female cytoplasm is i~. This corresponds to constitutivity. No repressor is present, and the enzyme is synthesized, thanks to the gene z+ introduced by the male. But the male has introduced at the same time the phase I • :/?-galactosidase X = repressor • X •. HOURS Figure 19. Synthesis of /3-Galactosidase by a Heterozygote. The heterozygote of type II shown in the preceding figure has been formed by the transfer of the male genes i+ z+ into the i~ z~ female. The female, being constitutive (i~), is devoid of repressor, and ^-galactosidase is synthesized, in the absence of an inducer, as soon as the gene z+ enters the female. This is the first phase. But the male has introduced also the inductive gene i+: a repressor is synthesized, and the synthesis of galactosidase stopped. This is the second phase. If, however, an inducer is added, the synthesis of the enzyme continues. gene i+, which, according to the hypothesis, should be responsible for the manufacture of a repressor. Something seems to be wrong. If, however, the synthesis of galactosidase is followed long enough, it is then found that the rate of enzyme synthesis decreases and reaches a zero value (Figure 19). A repressor has really been formed. [48]. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lwoff, André, 1902-. Cambridge, M. I. T. Press
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