. The physical basis of heredity . Heredity. SEX-CHROMOSOMES AND INHERITANCE 179 somes, including two Z's. The ^^^ that lacks a Z (8), fer- tilized by a sperm (8 -|- 1), makes a female with 17 chro- mosomes, including one Z. This scheme gives consistent results for sex-linked inheritance in birds. Since the daughter gets her single Z-chromosome from her father, she will show any sex- linked characters carried by his Z-chromosome. If the father carries a sex-linked dominant gene his sons and his daughters will be alike. It should be noticed that while Guyer's scheme gives the same results so fa
. The physical basis of heredity . Heredity. SEX-CHROMOSOMES AND INHERITANCE 179 somes, including two Z's. The ^^^ that lacks a Z (8), fer- tilized by a sperm (8 -|- 1), makes a female with 17 chro- mosomes, including one Z. This scheme gives consistent results for sex-linked inheritance in birds. Since the daughter gets her single Z-chromosome from her father, she will show any sex- linked characters carried by his Z-chromosome. If the father carries a sex-linked dominant gene his sons and his daughters will be alike. It should be noticed that while Guyer's scheme gives the same results so far as sex-link- Blackc^ Barred. Pi \ BarredcT Oackd Darredo Blacko Fig, 79,—Scheme showing the transmission of the sex-linked characters B =barred, and b = black in the cross shown in Fig. 78. age is concerned, as the one described by Seller for some moths, the machinery in the male is different in the two cases, while that in the female is presumably the same. In both the female is heterozygous for Z; in the moth the male is homozygous (ZZ), but in the bird the two Z's described by Guyer both go to one pole at one of the maturation divisions, and reduce at the other—a proce- dure not known in any other animal. In the reciprocal cross (Fig. 78) a black cock is bred to a barred hen. The sons are barred—like their mother— the daughters are black—like their father, criss-cross inheritance. When the barred F^ cock and the black hen. 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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