100 CHAPTER 7 



7.5. One child is hemophilic, his twin hrother is not. 



(a) What is the probable sex of the hemophilic twin? 



(h) Are the twins monozygotic? Explain. 



(c) Give the genotypes of both twins and of their mother. 



7.6. A hemophilic father has a hemophilic son. Give the most probable genotypes 

 oi the parents and child. 



7.7. A Drosophila male with cubitus interruptus wing venation, ebony body color, 

 and white eye color is mated to a pure wild-type female (normal wing venation, 

 gray body color, and dull-red eyes); then the F, females are crossed to males 

 like their father. Give the kinds and relative frequencies of genotypes and of 

 phenotypes expected among the offspring of the last cross. 



7.S. Are you convinced that all genes have their material basis in the chromosomes? 

 Explain. 



7.9. What reason can you give for believing that in Drosophila the Y chromosome is 

 lacking a gene present in the X chromosome? That the X is lacking a gene 

 present in the Y? 



7.10. List evidence in support of the theory that chromosomes contain the material 

 basis for genes. 



7.1 1. Has any evidence been presented that a chromosome carries more than one gene? 

 Explain. 



7.12. What proportion of all genes causing hemophilia type A is found in human males? 

 Justify your answer. 



7.13. Does a gene have to be hemizygous in one sex to be sex-linked? Explain. 



7.14. Two phenotypically wild-type Drosophila were mated in a vial. By accident all 

 but one F x was lost. The survivor was a male with white eyes, ebony body 

 color, and cubitus interruptus venation. Give the most probable genotypes of 

 the parents. 



7.15. Using pure stocks of Drosophila, yellow-bodied male by gray-bodied (wild-type) 

 female produced 1241 gray-bodied daughters, 1150 gray-bodied sons, and 2 

 yellow-bodied sons. The reciprocal mating produced 1315 gray daughters, 924 

 yellow sons, and 1 yellow daughter. Give the genetic and chromosomal makeup 

 of each type of individual mentioned. Discuss the relative viability and fertility 

 of the different chromosomal types. 



7.16. Females of Drosophila having a notch in their wing margins mated to wild-type 

 males gave the following F, results: 550 wild-type 9 9, 472 notch 9 9, 515 

 wild-type 6 6 . Explain these results genetically. 



7.17. A line of Drosophila pure for the sex-linked gene, coral (W") was maintained in 

 the laboratory for many generations. To demonstrate sex-linkage to a class, a 

 coral male was mated to a wild-type female, and all the F^ were as expected. 

 The reciprocal cross, between a coral female and a wild-type male, gave 62 coral 

 females and 59 wild-type males. Present a hypothesis to explain this unusual 

 result. How would you test your hypothesis? 



7.18. The wild-type eye shape in Drosophila is ovoid. A certain mutant, X, narrows 

 the eye. Using pure lines, and ignoring rare exceptions, mutant 9 X wild-type $ 

 produces mutant sons and daughters in ¥ x ; wild-type 9 X mutant S produces 

 wild-type sons and mutant daughters in Fj. 



Another mutant. Y, also narrows the eye. Using pure lines of Y and wild-type, 

 mutant 6 or 9 X wild-type 9 or 2 produces 2 mutant 6 $ and 9 9:1 wild-type 

 £ $ and 9 9. Discuss the genetics of mutants X and Y. 



