518 - Herediiy and Evolution 



winged fly is crossed with a short-winged 

 individual? 



15. What is a backcross experiment? Why is the 

 backcross so useful in genetics? 



16. Rough-coated guinea pigs crossed to smooth- 

 coated pigs produce only rough coated F x 

 offspring. What results would be obtained: 



a. by inbreeding the Fj individual 



b. by backcrossing one of the ¥ l pigs 



17. Twenty-five percent of the offspring of a cer- 

 tain pair of white sheep are black. What was 

 the genotype of the parents? 



18. Explain the statement that hereditary trans- 

 mission is particulate in characier. 



19. After many generations, what result would 

 be anticipated if one black sheep (see Ques- 

 tion 17) were introduced into a herd of pure- 

 bred (homozygous) whites: 



a. assuming the heredity to be particulate 

 (as it is) 



b. assuming a "blending type" of heredity 

 (as it is not) 



20. In summer squash, white fruit (Y) is domi- 

 nant to yellow ()'), and flat fruit (R) is domi- 

 nant to round ()). The selected parents are 

 a plant with white, flat fruit ()')', RR), and a 

 plant with yellow, round fruit. Specify the 

 phenotypes and genotypes and their respec- 

 tive ratios: 



a. in the F, generation 



b. in the F„ generation (inbreed the Fj 

 plants) 



c. among the offspring obtained by back- 

 crossing one of the F, plants 



21. An albino (pure white) guinea pig with a 

 rough coat is mated with a black one with 

 a smooth coat. The F, offspring are all black 

 and rough. What would be the genotype and 

 phenotvpe ratios in the F., generation? 



22. A heterozygous black, smooth haired guinea 

 pig (Question 21) is crossed to a white, 

 heterozygous, rough-haired mate. What phe- 

 notvpe and genotype ratios would be ex- 

 pected among the direct offspring of this 

 cross? 



23. Carefully differentiate between the members 

 of each pair of terms: 



a. the phenotvpe and the genotype of an 

 individual 



b. a homozygous and a heterozygous indi- 

 vidual 



C. sex chromosomes and autosomes 



d. sex linkage and ordinary linkage 



e. complete and incomplete linkage 



24. In tomatoes, red fruit (Y) is dominant to yel- 

 low (y) and tallness (D) is dominant to 

 dwarfism (d); the two pairs of genes have 

 their loci in the same pair of chromosomes; 

 and the linkage is complete. What pheno- 

 type and genotype ratios would be expected 

 among the direct offspring if both of the par- 

 ents are red (heterozygous) and tall (hetero- 

 zygous). 

 Assume that the linkage relation in the par- 



25 



d and that 



ents given in Question 24 is 

 the cross-over value between the gene pairs 

 is 10 percent. Specify the gametes of such a 

 parent and indicate the relative abundance 

 of each gamete type. 



26. In rabbits, black coat (B) is dominant to 

 brown (b) and long hair (S) is dominant to 

 short (,v). Derive the phenotypes and geno- 

 types to be expected when a heterozygous 

 long-haired pig is crossed to a brown short- 

 haired mate: 



a. assuming that the two gene pairs have 

 their loci in separate pairs of chromo- 

 somes 



b. assuming that the loci are in the same 

 pair of chromosomes and that the link- 

 age is complete 



27. Make a diagram to show how sex is inherited 

 in Drosophila (and in man and many other 

 organisms). 



28. What is the basis for referring to the Y chro- 

 mosome of Drosophila as a "dummy"? 



29. In the fruit fly, red eye (IT) is sex-linked and 

 dominant to white eye (w). Specify the dis- 

 tribution of eve color (a) among the males, 

 and (1)) among the females, derived from 

 each of the following crosses: 



a. white-eyed female X red-eyed male 



b. heterozygous red-eyed female x white- 

 eyed male 



c. heterozygous red-eyed female X red- 

 eyed male 



30. In man, normal vision (B) is dominant to 

 red-green color blindness (b), and this trait 

 is sex-linked. Specify the distribution of nor- 

 mal and defective eyes among the sons and' 

 daughters produced by each of the following 

 matings: 



a. color-blind mother and normal father 



