226 



HEREDITARY TRANSMISSION 



[CH. 



factors will be m, n, o.... Then if the part of A which 

 contains the factor M exchanges places with the part of a 



FIG. 28. Diagrams illustrating the hypothesis of " crossing-over " of 

 characters borne by chromosomes, from MORGAN. 



a d. Simple crossing-over ; b and c represent the chromosome as made up 

 of a series of microsomes each of which is supposed to bear one 

 character. 



e g. Illustrating double crossing-over. 



In consequence of the double cross-over, the character M is transferred 

 to the lower chromosome while W and Br remain in the upper. 



