47 <^ Organisms Are Products of Heredity and Environme?it unit ix 



Shake each jar to mix the beans that are in it. With your eyes closed pick 

 one bean out of each jar and put the two beans together as though the 

 cells were forming a fertilized egg. Make a record of the kind of "fer- 

 tilized egg'' you get. Return the beans to their jars, shake the jars and re- 

 peat. Do this until you have a record of many "fertilizations." How many 

 of each kind of offspring did you obtain? What ratio is this? 



4. A biologist, studying his experimental four-o'clock plants in the 

 greenhouse, discovered that he had 294 with white flowers, 3 1 1 with red 

 flowers, and 629 with pink flowers. They were all children of the same 

 parents. What was the gene make-up of the parents? How do you know? 



5. If the plants in Exercise 4 are the Fo of a cross, what were the grand- 

 parents (Pj) like? What genes did they have? How do you know? 



6. By using letters can you show the results of crossing Andalusian fowl 

 through the Fo generation if you start with a pure black and pure white? 

 See Figure 415. 



7. Diagram the guinea pig cross through the Fo generation. Since white- 

 ness is recessive how should you write the letter to represent it? 



8. Sorghum is a plant much like corn. If you can obtain seedlings that 

 are the Fo sjeneration of a cross between red-stemmed and green-stemmed 

 plants, find out how many are red-stemmed, how many are green- 

 stemmed. Which is dominant? What is the ratio? 



9. If purple and white Fo ears of corn are available, count how many 

 kernels there are of each color on one ear. What ratio do you find? 

 Which color seems to be dominant over the other? Add together the re- 

 sults obtained by other members of the class examining different ears. 

 What ratio do you obtain now? Can you explain this? 



10. By using a diagram show the results to the Fo of crossing a plant 

 which bears yellow seeds with one bearing green seeds (yellow is dom- 

 inant). Be sure to show dominance by using a capital letter. Explain how 

 each type of offspring in the Fo would look. What would be the ratio of 

 yellow to green? 



11. If a biologist were to cross tall garden peas (not permitting self- 

 pollination to take place), what offspring might he obtain? (This is a 

 catch question; study it carefully.) Explain your answer. Can you state 

 the "ratios"? 



12. Suppose that you have a black guinea pig. Black is dominant over 

 white. You wish to find out whether or not this is pure black or hybrid. 

 How could you find out by performing one kind of cross? You might 

 need to obtain many offspring before being sure. Use a diagram. (Will 

 it help you to know that this is called a backcross? ) 



13. Diagram the cross between pure long- winged and pure vestigial- 

 winged (LL X "vv) fruit flies to the second filial, Fo, generation. 



14. (Optional) You can demonstrate how chromosomes assort them- 

 selves when a primary sex cell with two pairs of chromosomes forms sex 

 cells. Imagine you are dealing with a dihybrid which has genes for red 



