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Quantitative Characters 



Could this situation be explained on the basis purely of polymeric 

 genes? Explain. 



8. Davenport has suggested that duplicate, cumulative, nondominant 

 genes might determine skin pigmentation in human beings and that two 

 loci are probably involved. If the contributing genes are Ci and C2, 

 what is the ratio of offspring from a cross between two mulattoes whose 

 genotype is C1C1C2C2? If Davenport's theory of skin color is correct, 

 could two dark-skinned people produce a white-skinned child, and could 

 two whites produce a child of darker skin? 



9. A small plant is 20 cm tall and a large one is 32 cm tall. They 

 differ by twelve genes at six loci. These genes are polymeric and each 

 adds one centimeter to height. The two plants are crossed. What is 

 the appearance of the Fi and F2 ? Draw each in the form of a frequency 

 polygon. Calculate the mean and standard deviation. 



10. A small plant is 20 cm tall and a large one is 32. The tall plant 

 has three dominant genes A, B, and C, each of which contributes 2 cm 

 to height. The small plant has three dominant genes D, E, and F, each 

 of which subtracts 2 cm from height. The large plant is AA BB CC dd 

 ee fj and the small plant is aa hb cc DD EE FF. What is the appearance 

 of the Fi and F2? Draw each in the form of a frequency polygon. Cal- 

 culate the mean and the standard deviation. Compare both generations 

 with those in problem 9. 



11. A small plant is 20 cm tall and a large one is 32. The large one 

 is AA BB CC dd and has three dominant genes each of which adds 2 cm 

 to the basic height. The small one is aa bb cc DD and has one gene, D, 

 which subtracts 6 cm from basic height. Plot the Fi and F2 and calcu- 

 late the mean and standard deviation of each. Compare with problems 

 9 and 10. 



12. Would the results in problems 10 and 11 be different if none of 

 the genes showed any dominance ? 



