Questions and Problems 365 



QUESTIONS AND PROBLEMS 



1. What character was used by Lang to illustrate his theory of poly- 

 meric genes? How many loci did he consider were involved? Does 

 Davenport's theory of the same character differ as to the number of 

 loci? Explain. 



2. Plant A is 20 cm tall and plant B is 70 cm tall. When these two 

 are crossed, the Fi is 45 cm tall. If the Fi plants are selfed and a very 

 large F2 population is raised, what would be the expected size of the 

 smallest plant, of the largest plant, and of the plants of greatest fre- 

 quency ? 



3. Let us suppose that the 50 cm difference in the last problem is 

 the result of ten polymeric genes at five loci. What are the genotypes 

 of the two parents and of the Fi? What are the phenotypes and geno- 

 types of the F2? 



4. Select various F2 plants. Show how the mean and variability of 

 the F3 families from them compare. What proportion of the F2 plants 

 would breed true? 



5. If a seedsman had the plants mentioned in question 2, how could 

 he establish races that were 20, 40, 45, 55, and 70 cm tall? 



6. The following data were obtained by Emerson and East for lengths 

 of ears in maize. Explain. Calculate all constants and their probable 

 errors. See Research Bulletin 2 of the Nebraska Agricultural Experi- 

 ment Station. 



Parent Class Centers in Centimeters 



Class 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 



Pi (1) 4 21 24 8 



3 11 12 15 26 15 10 7 2 

 1 12 12 14 17 9 4 



1 10 19 26 47 73 68 68 39 25 15 9 1 

 4 3 13 13 18 23 9 5 4 3 3 1 



6 9 10 8 18 14 26 24 28 12 10 4 



1 8 5 13 10 18 18 11 2 2 

 F3 (lES) 10 1 14 15 24 10 2 2 1 



7. Egg production in fowls is a quantitative character. Hays has 

 found that it differs in stocks that possess or lack certain other char- 

 acters as follows (data from Hays in Poultry Science) : 



