BIOCHEMICAL STUDIES OF HYBRIDS 301 



Most of the work was carried out on endosperm tissue which 

 is triploid, with one paternal and two maternal chromosome sets. In 

 these cases a "maternal" effect was frequently detected; that is, the 

 maternal bands were more concentrated than the paternal. The indi- 

 vidual bands of the hybrids were generally less intense, indicating 

 that the total amounts of esterases were the same. 



In contrast to the endosperm, when esterases of the diploid 

 plumule tissues of hybrid seedlings were examined, the "hybrid" 

 esterase band was usually more intense than the parental bands. 



In the words of the author, "There is no question but that the 

 hybrid bands found in the heterozygotes represent new enzyme types 

 not present in either parent." This work constitutes another example 

 of allelic interaction in protein synthesis. It would be of particular in- 

 terest to know whether the esterases are antigenic and, if so, whether 

 the hybrid esterases behave as a new antigen. 



The reference by Hall to hybrid substances reported from 

 birds cited earlier relates to work summarized by Irwin (1951) and 

 subsequent work in Irwin's laboratory. In extensive studies of sero- 

 logical relations in the Pearlneck dove {Streptopelia chinensis), the 

 ring dove (S. risoria) and their hybrids, Irwin found in the hybrids 

 all the antigens shared by the parental species and most of the charac- 

 ters specific to each parent. Moreover, all of the hybrids possessed a 

 "hybrid substance" not found in either parent. Evidence was obtained 

 that the species-specific antigens segregated in simple Mendelian 

 fashion, indicating that each was under control of a single gene. In 

 contrast, in backcross hybrids the "hybrid substance" behaved as 

 though it were composed of three sub-units, each of which was linked 

 to a separate Pearlneck chromosome. In examining Irwin's original 

 paper (Irwin and Cumiey, 1945) it is difficult to determine exactly 

 how Irwin interprets the genetic basis of the hybrid substance. He 

 states. 



The antigenic characters of the blood cells have been proposed to be 

 more or less direct products or at least primary products of their 

 causative genes. However, since the interactions of genes to produce 

 certain antigens in some species hybrids and within a species is used 

 to explain the experimental results it may be concluded that more 

 than one step from gene to antigen is sometimes, if not always, in- 

 volved." 



The key point is that apparently all genetic elements which combine 

 to produce the antigenic sub-units come from Pearlneck doves, but 

 only in the hybrid is the specific hybrid-type antigen present. Irwin 

 refers to "genes with duplicate effects in interaction located on 



