68 CHAPTER 5 



5.21. Suppose each gone represented by a capital letter causes a plant to grow an 

 additional inch in height, aabbceddee plants being 12 inches tall. Assume 

 independent segregation occurs tor all gene pairs in the following mating: 

 A a 1111 cc /)r/ 1.1. <aa bb CC Dd Ee. 



(a) How tall are the parents? 



(b) HOW tall will the tallest F, be? 



(c) How tall will the shortest F, be? 



(d) What proportion of all F, will be the shortest? 



(e) Is dominance and/or epistasis involved in this system? Explain. 



5.22. In selecting for a quantitative trait, is the desired phenotype established in a 

 pure line more easily when dominance does or does not occur? Explain. 



5.23. Measure the length of 10 lima beans to the nearest millimeter. Calculate the 

 variance of this sample. To what can you attribute the variance? 



5.24. Is it of any advantage to an organism to have a trait determined quantitatively, 

 that is. by many gene pairs, rather than qualitatively, that is, by principally one 

 or a few gene pairs? Why? 



5.25. How would you prove that you were dealing with multiple alleles rather than 

 multiple pairs of genes? 



5.26. In cattle a cross of a solid-coat breed and a spotted-coat breed produces a solid 

 coat in Fj. Among the individuals of the spotted breed there is considerable 

 variation, ranging from individuals that are solid-colored except for small white 

 patches to those that are white with small colored patches. Selection within this 

 breed can increase or decrease the colored areas. Discuss the genetic basis for 

 coat color in these two breeds of cattle. 



5.27. Discuss the number of gene pairs involved in the following case: Golden Glow 

 corn has 16 rows of kernels to the ear; Black Mexican has 8 rows. The F r is 

 phenotypically intermediate, having an average of 12 rows. The F 2 is pheno- 

 typically variable, ranging from 8 to 18 rows, with approximately one of each 

 32 ears being as extreme as either P,. 



5.28. The Sebight Bantam and Golden Hamburgh are pure lines of fowl which differ 

 in weight. Although the F, of crosses between these lines are fairly uniform and 

 intermediate in weight, one in about every 150 F 2 is clearly heavier or lighter 

 than either P 1 pure line. Suggest a genetic explanation for these results. 



