MODES OF INHERITANCE IN HYBRIDS 489 



6. Inheritance in reciprocal crosses 



It must be obvious to the reader that in these and other teleost 

 crosses reciprocal hybrids differ materially in many respects. It 

 has been shown repeatedly that in the majority of cases where 

 in the hybrid a character appears as a blend between that of the 

 two parents, it approximates more closely the maternal than the 

 paternal condition. There are, however, exceptions in which the 

 paternal influence predominates. Again we have cases in which 

 in one reciprocal cross a given character will be almost entirely 

 like that of one parent, whereas in the other reciprocal cross 

 we may have a mosaic or a blend of the two parental conditions. 

 There are also cases in which the male influence predominates 

 in both reciprocal crosses, but is less pronounced in one cross 

 than in the other. The facts do not admit of being classed in 

 the category of sex-linked characters, for all hybrids of a strain, 

 which presumably consists of equal numbers of males and females, 

 show the same conditions. Nor is the inequality of reciprocal 

 hybrids to be explained by assuming that there may be a partial 

 elimination of paternal chromatin, as was the case in Baltzer's 

 echinoderm hybrids, for we have abundant evidence that in all 

 of these Fundulus crosses the paternal chromatin functions nor- 

 mally. There is evidently a problem here the solution of which 

 demands a much larger range of data than has as yet been 

 obtained. I am for my own amusement positing a number of 

 tentative hypotheses that may or may not stand the test of 

 experiment, but shall not risk at present a premature display, of 

 a tendency to jump to conclusions. As it stands the problems 

 involved in the differences between reciprocal crosses are unsolved. 



