40 CHAPTER 3 



Mohr, O. 1 .. "Woolly Hair a Dominanl Mutanl c haractei in Man," J. Herod.. 23:345- 

 352, 1932. 



Neel, J. V., and Schull, W. J., Human Heredity, University of Chicago Press, 1954, 

 pp. 83 86, 89 91, 240 241. 



Stern. (.'.. Principles oj Human Genetics, 2nd Ed., San Francisco: Freeman, I960. 



QUESTIONS FOR DISCUSSION 



3.1. How would you recognize a line of garden peas that had become genotypically 

 pure for a given trait'.' 



3.2. Criticize the assumption that genes come only from pre-existing genes and do 

 not arise de novo. 



3.3. Differentiate between phenocopies and phenotypic overlaps. 



3.4. Does a parent lose its own genetic material when it is transmitted to progeny? 

 Defend your answer. 



3.5. Is it necessary to assume that genes are able to reproduce themselves? Explain. 



3.6. List all the assumptions required to explain a 3:1 ratio in F 2 on a genetic basis. 



3.7. A mating of a black-coated with a white-coated guinea pig produces all black 

 offspring. Two such offspring when mated produce mostly black but some white 

 progeny. Explain these results genetically. 



3.8. A cross of two pink-flowered plants produces offspring whose flowers are red, 

 pink, or white. Defining your genetic symbols, give all the different kinds of 

 genotypes involved and the phenotypes they represent. 



3.9. What operation was employed in studying the gene in the present chapter? Define 

 a gene in terms of size. 



3.10. Discuss the role of dominance in the study of genes. 



3.11. Do organisms that reproduce asexually have genes? Explain your answer. 



3.12. What relation has a gene to the phenotypic effect with which it is associated? 



3.13. Do you agree with the statement on p. 33 that a cross between two colorless 

 pea plants results in "all colorless progeny"? Why? 



3.14. Throughout this book the use of the word "heredity" and its derivatives has 

 been avoided. Why do you think this is, or is not, justified? 



3.15. What is the difference between the pedigree and family methods of investigation? 



3.16. What evidence is there that pigmentation (albinism vs. nonalbinism) is due to 

 genes that are segregating? 



3.17. Two nonalbinos marry and have an albino child. What is the chance that the 

 next child is albino? Nonalbino? That of the next two children, both are 

 albinos? Nonalbinos? One albino and one nonalbino? 



3.18. What proportion of three-child families, whose parents are both heterozygous 

 for albinism, have no albino children? All albino children? At least one albino 

 child? 



3.19. Would you conclude that the gene for woolly hair is completely dominant to 

 nonwoolly hair? Explain. 



