Linkage and Cross-over 



\6j 



Fig. 78. Linkage Shown by Back-cross of Hybrid 



Black body color sometimes appears among fruit flies as a muta- 

 tion, as does also the vestigial wing character. If two such mutants 

 are crossed the oflfspring will resemble the wild type of fly, since 

 gray body color and long wing are both dominant. If such a 

 hybrid is now mated with a fly having both mutant characters, 

 there will result two types of flies in the next generation (F^). 

 resembling the two single mutants. That is, the characters that 

 went into the combination together come out together. If there were 

 independent assortments there should result four types of flies. 

 Compare the result of the second mating with the first one shown 

 in Figure jj. From Morgan, The Physical Basis of Heredity, pub- 

 lished by J. B. Lippincott Company. 



