mate with the emerging hybrid flies. ^ For the second generation, simply transfer 

 several hybrid male and female flies to new bottles. Again remove the adults after 

 they have laid their eggs. 



6 To study the inheritance of traits in poultry, incubate hybrid eggs of known 

 parentage and brood the chicks in the classroom or at home. (The inheritance of the 

 barred factor in the sex-chromosome can be demonstrated by crossing a Rhode 

 Island Red rooster and a Barred Rock hen.) Describe appearance of cockerels and 

 pullets. Account for the results you obtained. 



7 To trace the probable inheritance of human traits, collect evidence as to the 

 occurrence of various traits in the members of a family. Distinguish those character- 

 istics which seem certainly to be inherited as dominant or as recessive. Note any 

 evidence that a trait may be inherited but remain undeveloped under special condi- 

 tions. Note any evidence as to whether a child inherits more traits from the parent 

 of the same sex than from the parent of the opposite sex. 



QUESTIONS 



1 How has hybridizing been used to Improve our plants and animals.'' What 

 are its advantages.? its Hmitations? 



2 What is it that actually continues from one generation to the next, in sexual 

 reproduction.^' 



3 How can the changes in the chromosomes be related to the simple Mendelian 

 laws of dominance, segregation, and independent assortment.'' 



4 In what sense are the facts of linkage, imperfect dominance, and multiple 

 factors exceptions to the Mendelian laws.i^ 



5 How does a further study of these seeming exceptions strengthen the hypoth- 

 esis that the bearers of heredity are in the chromosomes? 



6 How is it that individuals sometimes lack qualities which are present in one 

 or both of the parents? 



7 How can an individual sometimes manifest qualities which neither of the 

 parents has? 



8 How do the common fruits and vegetables in use today differ from those of a 

 generation ago? How did the changes come about? 



9 What are the necessary steps in establishing a new breed of plants or animals? 



10 What advantages has the plant-breeder over the animal-breeder? 



11 How does our present knowledge of heredity agree with the idea that off- 

 spring inherit the effects of experience, exercise, injury, sickness, and other modifica- 

 tions? 



12 In what way can the experience or condition of a pregnant female influence 

 the offspring? 



^ Ordinarily it takes about two weeks for the fruit fly to complete its life cycle, though in an 

 incubator at from 75° F to 80° F it takes from 10 to 12 days. 



505 



