. The physical basis of heredity . Heredity. 166 PHYSICAL BASIS OF HEREDITY At the time when the polar bodies are extruded from the egg, the two X's separate, one passing out, the other remaining in the egg. Every egg is left with one X (Fig. 68). In the male, the X and Y conjugate and separate at one of the maturation divisions, so that each sperm contains either an X- or a F-chromosome (Fig. 68). Fertilization of any egg {X) by an X-bearing sperm produces a female 9 XX cT XV FiQ. 68.—Scheme showing the relation of the sex-chromosome to sex-determination. XX-XY type. {XX). Fertilizat
. The physical basis of heredity . Heredity. 166 PHYSICAL BASIS OF HEREDITY At the time when the polar bodies are extruded from the egg, the two X's separate, one passing out, the other remaining in the egg. Every egg is left with one X (Fig. 68). In the male, the X and Y conjugate and separate at one of the maturation divisions, so that each sperm contains either an X- or a F-chromosome (Fig. 68). Fertilization of any egg {X) by an X-bearing sperm produces a female 9 XX cT XV FiQ. 68.—Scheme showing the relation of the sex-chromosome to sex-determination. XX-XY type. {XX). Fertilization of any egg (Z) by a F-bearing sperm produces a male {XY). Since the two kinds of spermatozoa are produced in equal numbers, females and males will be equal in num- ber. The mechanism is self-perpetuating. The Inheritance or Factors Carried by the Sex- Chromosomes in the Deosophila Type Since the son gets his one X-chromosome from his mother, and the Y from his father, he inherits factors carried by the sex-chromosomes in a different way from. 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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