Heredity and sex . 244 HEREDITY AND SEX two such individuals are normal, but the color blindnessreappears in one-fourth of the grandchildren, and inthese only in the males. The reverse mating is shownin the next diagram in which the female is will have color-blind sons and normal daughters(criss-cross inheritance), and all four kinds of grand-children. Other cases in man that are said to show sex-linkedinheritance are atrophy of the optic nerve, multiple cTT^ *P iSiiiiiliitiiiii. Fig. 118. — Pedigree of night blindness in a negro family from Bordley. (After Davenport.) sclerosi
Heredity and sex . 244 HEREDITY AND SEX two such individuals are normal, but the color blindnessreappears in one-fourth of the grandchildren, and inthese only in the males. The reverse mating is shownin the next diagram in which the female is will have color-blind sons and normal daughters(criss-cross inheritance), and all four kinds of grand-children. Other cases in man that are said to show sex-linkedinheritance are atrophy of the optic nerve, multiple cTT^ *P iSiiiiiliitiiiii. Fig. 118. — Pedigree of night blindness in a negro family from Bordley. (After Davenport.) sclerosis, myopia, ichthyosis (Fig. 116), muscularatrophy (Fig. 117), and night-bhndness (Fig. 118).There are also other cases in man that appear to comeunder the same category, but for which the evidenceis not so clear. All these cases of sex-linked inheritance in manare explained by the assumption that the factor thatproduces these characters is carried by the sex chromo-some, which is duplex (XX) in the female and simplex(X) in the male. A simpler assumption has not yetbeen found. If one is fastidious and objects to the SPECIAL CASES OF SEX-INHERITANCE 245 statement of factors being carried by chromosomes, hehas only to say, that if the factors for the charactersfollow the known distribution of the sex chromosome,the results can be accounted for. The culmination of the evidence of sex-determina-tion in man is found in a study of the cell structureof the human race itself. Strange as it may
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Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectsex, bookyear1913
