Heredity — Genetics 7l9 



15. Why do parents have duplicate genes for each specific character? From what 

 source has each been received ? Why, in the production of sex cells or gametes 

 by parents, is it necessary to separate or segregate the allelomorphic genes? 

 What happens when they are not segregated? 



16. List reasons why it is desirable for each parent to contribute a gene for each 

 character. 



17. Do parents contribute equally to their offspring or do they merely have equal 

 opportunity to contribute? Explain your statement. 



18. Explain the difference between incomplete dominance and complete domi- 

 nance. 



19. Explain the phenomena of linkage and crossing-over. What are the results 

 which follow each of these phenomena? 



20. Contrast sex-linked and sex-influenced characters. Give several illustrations 

 of each. 



21. Discuss and give examples of the different types of chromosomal aberrations. 



22. What are the chief causes of mutations? What are their chief characteristics? 

 What benefits might be derived from mutations ? 



23. Explain how sex is determined. What has this to do with heredity? 



24. Explain Weismann's theory of the continuity of germ plasm. Of what impor- 

 tance is this in heredity? Explain the origin of somatoplasm. 



25. Explain all the more important stages in the production and maturation of 

 germ cells. How does this affect heredity? Define meiosis and contrast with 

 normal mitosis. Of what importance is synapsis in genetics ? 



26. List several human traits, telling which is dominant and which is recessive. 



27. Problems in heredity: 



Work the following problems in guinea pig inheritance using the following 

 symbols: B, black hair; b, white hair; R, rough coat of hair; r, smooth coat of 

 hair; S, short hair; s, long hair. 



(a) Work out the entire monohybrid cross in the following by using the proper 

 symbols. Carry through to the F2 generation in each case: (1) Homozygous 

 rough X homozygous rough; (2) homozygous rough X smooth; (3) hetero- 

 zygous rough X heterozygous rough; (4) heterozygous rough X smooth. 



(b) Work out the entire dihybrid cross through the F2 generation using the cor- 

 rect symbols in the following : ( 1 ) Homozygous black-rough X homozygous 

 black-rough; (2) homozygous black-rough X white-smooth; (3) heterozygous 

 black-rough X heterozygous black-rough; (4) white-smooth X white-smooth. 



(c) Work out the entire trihybrid cross through the F2 generation using the correct 

 symbols in: (1) BbRrSs X BbRrSs; (2) BBRRSS X bbrrss; (3) BbRRSs X 

 bbRrSs; (4) bbrrSs X bbRrss; (5) bbrrss X bbrrss. 



Work out the following problems in the inheritance in peas, using the following 

 symbols: T, tall plant, t, dwarf plant; Y, yellow seed; y, green seed; R, round, 

 smooth seed; r, wrinkled seed. 



(a) Work the following monohybrid crosses as above: (1) Homozygous tall X 

 dwarf; (2) heterozygous tall X heterozygous tall. 



(b) Work out the following dihybrid crosses as above: (1) Homozygous tall- 

 round X dwarf -wrinkled ; (2) heterozygous tall-round X heterozygous tall- 

 round; (3) homozygous tall-round X heterozygous tall-round. 



