568 GENETICS AND EVOLUTION 



genes within a given chromosome, have been made (Figs. 32.7 and 32.8). 

 The only human chromosome which has been even partially mapped is 

 the sex chromosome. 



Questions 



1. Define in your own words: dominant, recessive, homozygous, heterozygous, genotype, 

 phcnotype, gene, allele, locus and back-cross. 



2. Discuss Mendel's studies of heredity as an example of the scientific method. 



3. Give briefly the implications of Mendel's two laws of heredity. 



4. In peas, the gene for smooth seed coat is dominant to the one for wrinkled seeds. What 

 would be the result of the following matings: heterozygous smooth x heterozygous 

 smooth? Heterozygous smooth x wrinkled? Heterozygous smooth x homozygous 

 smooth? Wrinkled x wrinkled? 



5. In peas, the gene for red flowers is dominant to the one for white flowers. What would 

 be the result of mating heterozygous red-flowered, smooth-seeded plants with white- 

 flowered, wrinkled-seeded plants? 



6. The mating of two black, short-haired guinea pigs produced a litter which included 

 some black, long-haired and some white, short-haired offspring. What are the geno- 

 types of the parents and what is the probability of their having black, short-haired 

 offspring in subsequent matings? 



7. Human color-blindness is a sex-Hnked, recessive trait. What is the probability that a 

 woman with normal vision whose husband is color-blind will have a color-blind son? 

 a color-blind daughter? What is the probability that a woman with normal vision 

 whose father was color-blind but whose husband has normal vision will have a color- 

 blind son? a color-blind daughter? 



8. The gene for white eye color (w) in fruit flies is sex-linked and recessive to normal red 

 eye color (W). Give the results of mating (a) a heterozygous, red-eyed female with a 

 red-eyed male, (b) a white-eyed female with a red-eyed male and (c) a heterozygous, 

 red-eyed female with a white-eyed male. 



9. A blue-eyed man, both of whose parents were brown-eyed, marries a brown-eyed 

 woman whose father was blue-eyed and whose mother was brown-eyed. Their first 

 child has blue eyes. Give the genotypes of all the individuals mentioned and give the 

 probability that the second child will also have blue eyes. 



10. Outline a breeding procedure whereby a true-breeding strain of red cattle could 

 be established from a roan bull and a white cow. 



11. Suppose you learned that shmoos may have long, oval or round bodies and that mat- 

 ings of shmoos gave the following results: 



long X oval gave ,'j2 long and 48 oval 

 long X round gave 99 oval 

 oval X round gave 51 oval and 50 round 

 oval X oval gave 24 long, 53 oval and 27 round. 

 What hypothesis about the inheritance of shmoo shape would be consistent with 

 these results? 



Supplementary Reading 



Ihere are several good elementary textbooks of genetics which provide further read- 

 ing for those interested in the subject: L. H. Snyder's The Principles of Heredity, E. O. 

 Dodson's Genetics, R. B. Goldschmidt's Understanding Heredity and Srb and Owen's 

 General Genetics. Ynii and Heredity, by A. Scheinfeld, is a popular account of the inheri- 

 tance of human characters. Curt Stern's Principles of Human Genetics is a clear, well- 

 written text of general genetics with special emphasis on human inheritance. 



