Multiple Alleles; Multigenic Traits 67 



5.5. Give examples of complete dominance and of no dominance as found in human 

 beings. 



5.6. Is the occurrence of complete dominance helpful in determining the genetic basis 

 of alternatives for a given trait? Explain. 



5.7. A father with blood group types M and O has a child with MN and B blood types. 

 What genotypes are possible for the mother? 



5.8. Criticize the statement: "Genes can be explained on the basis of a presence-or- 

 absence hypothesis." 



5.9. A woman belonging to blood group B has a child with blood group O. Give their 

 genotypes and those which, barring mutation, the father could not have. 



5.10. What do you think of the view that all the different genes that exist can be 

 described as being different multiples of a single basic unit which is capable of 

 retaining its integrity and is able to self-replicate? 



5.11. How many different genotypes are possible when there are four different alleles 

 of a single gene? 



5.12. Does the discussion of multiple alleles in the text imply that: (a) There is an 

 infinite variety of isoalleles? (b) No two genes are ever identical? Explain. 



5.13. Describe how you would test whether the genes for white eye color in two 

 different populations of Drosophila were alleles, isoalleles, or nonalleles. 



5.14. In rabbits the following alleles produce a gradation effect from full pigmentation 

 to white: agouti (C), chinchilla (c rh ) and albino (c). Another allele, c h , pro- 

 duces the Himalayan coat-color pattern. C is completely dominant to all these 

 alleles, c h is completely dominant to c, whereas c clt shows no dominance to 

 c h or c. 



(a) How many different diploid genotypes are possible with the alleles men- 

 tioned? 



(b) A light chinchilla mated to an agouti produced an albino in F x . Give the 

 genotypes of parents and F 1 . 



(c) An agouti mated to a light chinchilla produced in F x one agouti and two 

 Himalayan. Give the genotypes possible for parents and Fj. 



(d) An agouti rabbit crossed to a chinchilla rabbit produced an agouti offspring. 

 What genotypic and phenotypic results would you expect from crossing the 

 F 1 agouti with an albino? 



5.15. For each of the following matings involving Nicotiana give the percentage of 

 aborted pollen tubes and the genotypes of the offspring. 



$ 9 6 9 



(a) sls2Xsls3 (c) si s4 X si s4 



(b) sls3Xs2s4 (d) s3 s4 X s2 s3 



5.16. Could you prove the existence of multiple allelism in an organism that only re- 

 produces asexually? Explain. 



5.17. Do the genes for quantitative traits show epistasis? Explain. 



5.18. Does the environment have a more important role in determining the phenotype 

 in cases of quantitative than in cases of qualitative traits? Explain. 



5.19. Under what circumstances are only seven phenotypes possible when three pairs 

 of genes determine a quantitative trait? 



5.20. Discuss the statement: No new principles of genetics have originated from the 

 study of polygenic traits. 



