484 Orgams7}iS Are Fro ducts of Heredity aiid Environment unit ix 



fertilized tg^} How does the animal look? Suppose that only one such 

 animal appeared. What would have to be done to obtain more of the 

 white animals? Use a diagram to illustrate. 



2. Suppose a changed gene were dominant to the normal. Hornlessness 

 appeared as a dominant mutation in a breed of cattle. Show by letters 

 what must be done to get a pure breed of hornless cattle. (Let {h) repre- 

 sent horned condition, (H) represent hornlessness.) 



3. Draw diagrammatically the normal mitosis which occurs (after re- 

 duction division from four to two) making a gamete which has two chro- 

 mosomes. Then show by means of a series of diagrams what might hap- 

 pen to produce a gamete which has twice as many chromosomes as it 

 would normally have. 



4. Summary. You will find it easy to make this summary. Read the 

 paragraph titles carefully. What is the one main topic under which the 

 others will fit as subtopics? Write your outline and fit in the few neces- 

 sary facts briefly. The last paragraph, though short, is extremely impor- 

 tant and might well stand as a second main topic. 



Further Activities in Biology 



1. Consult some textbook in genetics such as Snyder or Sinnott and 

 Dunn (see bibliography) to discover how many of the mutations that 

 have appeared in the fruit fly are dominant, how many are recessive, and 

 how many are unfavorable to the species. 



2. Jaffe's Ojit posts of Sciejice contains some interesting information 

 about Morgan and Muller. 



3. Demonstrate to the class the various types of chromosomal changes 

 by using plasticine of various colors. 



4. What kinds of mutations have taken place in corn, in the soybean, 

 or in other cultivated plants? Prepare a report for the class. (The Year- 

 book of Agriculture, 1936, 1937, contains information.) 



