. The physical basis of heredity . Heredity. SEX-CHBOMOSOMES AND INHERITANCE 201 are given off by tlie egg are shown in the next diagram (Fig. 93). One X may go out of the egg, and the other X and the Y stay in; or one X may stay in the egg and the other X and the Y go out. In these two cases, X and X may be thought of as members of a pair that conjugate, as in the normal female, and then separate, and chance alone determines whether the Y stays in or passes out. Again Y may go out of the egg and X and X stay in; or X and X raiAR BODY EGGS SPERM. I F^Q J (exception) 4 Fia. 93.—Non-disjunction.
. The physical basis of heredity . Heredity. SEX-CHBOMOSOMES AND INHERITANCE 201 are given off by tlie egg are shown in the next diagram (Fig. 93). One X may go out of the egg, and the other X and the Y stay in; or one X may stay in the egg and the other X and the Y go out. In these two cases, X and X may be thought of as members of a pair that conjugate, as in the normal female, and then separate, and chance alone determines whether the Y stays in or passes out. Again Y may go out of the egg and X and X stay in; or X and X raiAR BODY EGGS SPERM. I F^Q J (exception) 4 Fia. 93.—Non-disjunction. In the upper part of the figure the four posaible modeB of elimination of the sex-ohromosome from XXY eggs are shown; the results of their fertili- zation by an X-bearing sperm of the male is shown below. go out and Y stay in. Here X and Y may be supposed to be members of the conjugating pair, and the free X goes to the same pole as the X that conjugated. In the diagram, each of these four types of eggs is represented as fertilized by an X-bearing sperm. In order to make the outcome more apparent the original XXZ female may be supposed to have had white eyes (clear X's) and the male that fertilized her red eyes (here repre- sented by the black X carrying the gene for red eyes). Four classes of individuals are expected: (1) Bed-eyed females (XXF); (2) red-eyed females (XX); (3) red-eyed. 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 Morgan, Thomas Hunt, 1866-1945. Philadelphia : Lippincott
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