LINKAGE 173 



We may now consider some further examples of linkage. 

 In the plant, Primula sinensis, Gregory observed the oc- 

 currence of linkage in a group of five characters, viz. 



Dominant Recessive 



1. Short style vs. long style (1). 



2. Magenta corolla vs. red corolla (r). 



3. Tinged corolla vs. full-colored corolla. 



4. Green stigma vs. red stigma (s). 



5. Pale stem vs. full red stem. 



Altenburg later determined the strength of the linkage ex- 

 isting between three of these five pairs of characters, viz., 1, 

 2, and 4 of the above list. His results may be expressed in 

 a linkage map as follows: 



34.0 45.6 



The cross-over percentage between 1 and r was found to be 

 34.02, between r and s, 11.62. The sum of these two, 45.64, 

 is the total (uncorrected) map distance. The observed cross 

 over percentage between 1 and s was 40.6, which falls short 

 of the map distance by almost exactly the amount indicated 

 by Haldane's table. 



In the sweet pea the earliest discovered examples of link- 

 age are found. Here are known two linkage groups con- 

 taining each three pairs of characters as follows: 



Group I. 



Group II. 



Results described by Bateson and by Punnett indicate that 

 in Group I the map relations of the three genes are: 



E-B L 



.78 12.5 



The group is a compact one, with E and B very closely 

 linked, cross-over percentage less than one, with B and L 



