. Biological order. Biology. X X X X X ^ v- X X X 2+ X X I I 5^ X X X X ^X X "" X ^ X X X > cr zygote I. X X X "^ X X z + X x^ X X X X X X X X X X X X X ? i- z- . > 'T^ > zygoteH ' 9 • • • • • • l'"^ z + • > • • • • Figure 18. The Repressor. I. The constitutive male i~ does not manufacture enzyme in the absence of an inducer because it is z~. The inductive female i+ does not manufacture enzyme in the absence of inducer, despite the presence of z+, because a re- pressor is present (repressor is represented by crosses). The corresponding zygote (zygote I) does not
. Biological order. Biology. X X X X X ^ v- X X X 2+ X X I I 5^ X X X X ^X X "" X ^ X X X > cr zygote I. X X X "^ X X z + X x^ X X X X X X X X X X X X X ? i- z- . > 'T^ > zygoteH ' 9 • • • • • • l'"^ z + • > • • • • Figure 18. The Repressor. I. The constitutive male i~ does not manufacture enzyme in the absence of an inducer because it is z~. The inductive female i+ does not manufacture enzyme in the absence of inducer, despite the presence of z+, because a re- pressor is present (repressor is represented by crosses). The corresponding zygote (zygote I) does not produce enzyme in the absence of an inducer, despite the presence of the constitutive gene i~, because the cytoplasm of the inductive female contains a repressor. The gene i+ is dominant. II. The inductive male does not manufacture enzyme in the absence of an inducer because a repressor is present. The constitutive female does not manu- facture the enzyme because it is z~. The corresponding zygote (zygote II) will produce enzyme for a limited time (see next part of figure), because the z+ gene coming from the male has entered into a constitutive cytoplasm (devoid of repressor). The two zygotes (I and II) have the same genetic constitution, but zygote I has an inductive cytoplasm (the female is i+), whereas zygote II has a consti- tutive one (the female is i~). [47]. 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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