Questions and Problems 123 



12. A green-silked maize plant is crossed with a salmon-silked plant. 

 The offspring segregated into 220 green and 180 salmon. Is the devia- 

 tion significant? 



13. If the offspring in problem 12 segregated into 420 green and 380 

 salmon, is the deviation significant ? Here the deviation is the same but 

 the sample is larger. Why should this make any difference? 



14. Using the same number of plants in problem 12 (400 plants), what 

 must be the deviation from expected to give the same value of x^ as 

 was obtained in problem 13? 



15. In the following six experiments (Wright in Genetics) the size of 

 the family and the percentage of males obtained in each experiment are 

 listed. Determine by the method of the standard error whether males 

 and females are produced in equal proportions in the guinea pig. 



Number of Per Cent 



Experiment Individuals of Males 



(AB)B 486 47.9 



(AD)D 359 45.7 



(AF)F 417 48.9 



(AE)E 230 55.7 



(BD)2 380 47.9 



(CD)2 285 46.7 



16. In guinea pigs, gene p produces pink eye and P produces black. 

 Wright crossed two animals which were supposedly heterozygous and 

 obtained 197 black and 90 pink. Calculate how much greater is the 

 deviation than the standard error. Can this be considered a true 

 example of a 3 : 1 ratio? If not, how do you explain the ratio obtained? 

 Could such a result possibly be explained as an extreme chance devia- 

 tion? Consult Wright's paper for his explanation. 



17. Determine the probability that the observed ratio in problem 16 

 is a true example of a 3 : 1 ratio by the x^ method. 



