1 1 1 1 1 ! 



r hB , I II I 



Each B represents a 



zygote with two chromosomes. 

 Gene order is as follows. 



<^ and S 88 SI V 



Example: B=^t|^# 88 II II S 



f-jS2a ■■"■ ZS 



'^gpgS akimm nan 



** 818 ** 

 Q^ 23S8 S2 



^^ 88&S SS 



rprj B3S rjri 

 OQ C2DCP DCCri 



^^ ESS *^^ 



a 



SS SS es eg 



S 8B 8 



J I L 



1 2 3 4 5 6 



Plate 2. Diagram showing all the possible recombinations which could 

 be obtained in an F2 for a pair of segregating chromosomes {AiBiCiDiEiFi, 

 diagrammed in white, vs. A2B2C2D2E2F2, diagrammed in black). Each 

 dumbbell represents a different genotype and diagrams the two chromo- 

 somes of which it is made up, one above and one below. The genes A, 

 C, and E affect a character whose values are measured on the horizontal 

 axis. The genes B, D, and F affect another character whose values are 

 measured on the vertical axis. All the possible recombinations in such 

 an F2 are shown to form a "recombination spindle" passing from the 

 corner (0, 0) that was characteristic of one species to the corner (6, 6) 

 that was characteristic of the other. Comparative frequencies of the re- 

 combinations not considered. Further explanation in the text. 



40 



