. The physical basis of heredity . Heredity. 178 PHYSICAL BASIS OF HEEEDITY her black color to only half of her grandsons. The chro- mosomal explanation can obviously be worked out on the same scheme as in Abraxas (Fig. 77). But if Gruyer's recent account of spermatogenesis in birds is correct, the situation is different. Guyer describes the ripening of the sperm as follows: There are 18 chromosomes in the male, including two large Z's (16 + 2). After synapsis there are 9 double chromosomes in the first spermatocyte, all of which, except ZZ separate at the first maturation division, 8 going to
. The physical basis of heredity . Heredity. 178 PHYSICAL BASIS OF HEEEDITY her black color to only half of her grandsons. The chro- mosomal explanation can obviously be worked out on the same scheme as in Abraxas (Fig. 77). But if Gruyer's recent account of spermatogenesis in birds is correct, the situation is different. Guyer describes the ripening of the sperm as follows: There are 18 chromosomes in the male, including two large Z's (16 + 2). After synapsis there are 9 double chromosomes in the first spermatocyte, all of which, except ZZ separate at the first maturation division, 8 going to one pole and 8 to the other. One BaTredcT. zV zV Barredd* Barred d* Barred o Black: o Fig. 77.—Scheme showing the transmission of the aex-linked characters B =barred, and b =black in the cross shown in Fig. 76. daughter cell gets both Z's (8 + 2). This cell then divides again, the Z's presumably separating so that two second spermatocytes are produced, each with 9 chromosomes (8+1), including the Z. These become the functional sperm. The other spermatocyte, the one without a Z, may divide again, but it, or its products, degenerate, and never produce sperm. According to Guyer, there are 17 chromosomes in the female, including one Z. Presum- ably, then, after reduction half of the eggs- will contain a Z (8 + 1), the other half will be without it (8). The egg that carries a Z (8 + 1), fertilized by a sperm (each sperm carries a Z (8 + 1)), wiU make a male with 18 chromo-. 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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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherphiladelphialippin
