PROBLEM 5. Breedmg New Types of Aiibnals mid Plants 505 



one organism the desirable characters of this he will inbrced. If he is dealing with 



one parent and the desirable characters certain kinds of plants, it is not necessary 



of the second parent. to fix the type for he may resort to vcgc- 



The breeder's final step after he has ob- tative propagation. By these methods ma 



tained a desirable mutant or a successful has made great in^provements in tl.c 



hybrid is to "fix the type." He must be plants and animals he makes use of f(;r 



able to get more of the same kind; to do many purposes. 



Questions 



1. Through the centuries there has been progress in the breeding of 

 some animals. Which? Why is there more rapid progress in recent 

 times? 



2. Show that selecting the best gene combination is a method of getting 

 better types of organisms; name a specific plant and mention a specific 

 improvement. 



3. When must the breeder expect to find that no further improvement is 

 possible by this method? 



4. What, in general, enables biologists to decide that two organisms are 

 members of the same or different species? What does the plant 

 breeder usually call the subdivisions of a species? What name does the 

 animal breeder commonly use for them? 



5. State how one breed of cows was improved within forty years. Ex- 

 plain inbreeding. Of what importance is it in animal breeding? 



6. State possible advantages and disadvantages in inbreeding and also in 

 outbreeding. In which organisms can one obtain pure forms through 

 continued inbreeding? 



7. What is a pedigree? How is it made use of by the breeder? 



8. Name two animal mutations and several plant mutations which have 

 been preserved because of their desirability. Name two methods of 

 getting new or improved types of plants and animals. 



9. Give two examples of new varieties or kinds of animals which were 

 developed by hybridization. For each one tell what traits the breeders 

 were seeking and what animals were used to supply these traits. 



10. Explain how hybridization and selection produced an improved sugar 

 cane and the Shasta daisy. How does the breeder frequently obtain de- 

 sirable parents? 



1 1 . Explain why vegetative propagation is a great advantage to the 

 breeder. 



12. Explain grafting, using the terms stock and scion. Explain why graft- 

 ing is a help to breeders of certain kinds of plants. 



13. To what extent is a good environment important to the breeder? 



14. Review briefly the three methods used to get new and improved types 

 of animals and plants. 



