88 



BIOCHEMICAL SYSTEMATICS 



"half-homologous" extracts. For example, if one wishes to form a half- 

 homologous antiserum to a plant of the genotype S2-3, an antiserum 

 is prepared against S2-3 serum and pre-adsorbed with S2-4 serum. In 

 the first reaction the common proteins, including the S2 antigen are 

 precipitated, leaving in the antiserum, presumably, only the S3 anti- 

 bodies. Another S2-3 pollen extract is then said to be "half- 

 homologous" with the antiserum, and an 82-6 extract is said to be 

 "heterologous." In the latter case no reaction, or at most a very slight 

 reaction, may be expected. The results of a series of cross reactions 

 are shown in Fig. 5-3. The figures within the squares represent the 

 time, in minutes, required to form a precipitin ring; therefore the 

 lower values indicate the stronger reaction. A blank indicates that the 

 reaction was not recorded. Certain inconsistencies are presumed to 

 result from extraneous genie differences in the material since the 

 stocks were not isogenic. However, these gene differences were obviously 

 not sufficient to prevent generally good correlations. 



TA S 



2.6 



»3.4 



>3.6 



J3.6 



S4.6 



^2.4 



>2.3 



AS AA 



S3.6 S2.4 



S3.4 S2.6 



S3.4 S3.6 



S3.4 S4.6 



S2.4 S36 



S2.4 S3.6 



S2.6 S3.4 



S2.6 S4.6 



Fig. 5-3. Time in minutes to form a ring precipitate at ^ dilution of test antigen (TA). 

 Antiserum is designated AS, and the adsorbing antigen is designated AA. 



B = Heterologous antigen, that is, no S alleles common to test antigen and adsorbed serum. 



n = Completely homologous, that is, both S alleles common to test antigen and adsorbed serum. 



D = Half-homologous, that is, one S allele common to test antigen and adsorbed serum. 



I I = Untested combinations. 



