. Comparative physiology. Physiology, Comparative; Physiology, Comparative. 190 COMPARATIVE PHYSIOLOGY pj Ft by genetical factors for which one sex is heterozygous, so that a I : I sex ratio is maintained by the normal consequences of a homozygous-heterozygous mating. Since in this case maleness is the state associated with the single condition and femaleness with the duplex state as regards the sex-linked genes, the male may be represented symbolically as F/ and the female as FF, using the symbol F for that which determines femaleness. This type of sex-linked inheritance occurs in most insect
. Comparative physiology. Physiology, Comparative; Physiology, Comparative. 190 COMPARATIVE PHYSIOLOGY pj Ft by genetical factors for which one sex is heterozygous, so that a I : I sex ratio is maintained by the normal consequences of a homozygous-heterozygous mating. Since in this case maleness is the state associated with the single condition and femaleness with the duplex state as regards the sex-linked genes, the male may be represented symbolically as F/ and the female as FF, using the symbol F for that which determines femaleness. This type of sex-linked inheritance occurs in most insects and in mammals ; and for reasons given later may be anticipated to occur in practically all higher bi- sexual animals except birds and lepidoptera (moths and butterflies). The phenomenon of sex-linked in- heritance was first discovered in the latter group by Doncaster (1906). A variety of the currant moth Abraxas grossulariata is distin- guished by the pale colour of the wings as lacticolor. If a lacticolor female (wings of a pale cream tint) is crossed with the normal dark- winged (grossulariata) male, all the offspring of both sexes are of the grossulariata type : in the there is a 3:1 ratio of grossulariata to lacticolor, but all the males are of the grossulariata type. In the reciprocal mating the grossu- lariata female can only transmit the grossulariata pattern to her sons ; all the female offspring are of the lacticolor type. When the are mated inter se^ equal numbers of lacticolor and grossulariata males and females are produced (diagram). Here the female moth is constitutionally simplex with respect to the sex-Hnked genes. This is the exact reverse of the state of affairs in sex-linked characters in Drosophila. Femaleness is associated with the simxplex condition of genes which in the duplex condition give rise to maleness. The predetermination of sex by genetic factors does not. Fig. 42.—Sex-linked inherit- ance in Please note that these image
Size: 1099px × 2274px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysiologycomparativ
