44 A MANUAL OF MENDELISM 



But, by their progeny, the hybrids showed that they 

 were really of two different kinds — the differences 

 resulting from other factors still — for, while some threw 

 greys and albinos only, others threw blacks in addition ; 

 and, since the yellow-grey parents were known to be all 

 of one kind, the differences in the hybrids must have 

 been due to differences among the parent albinos. 

 Thus, since there are at least two kinds of albinos, they 

 must carry between them more than one factor whose 

 effects are invisible. 



The progeny thrown by the two kinds of hybrids are 

 shown in the tables on page 45. 



If the progeny of the hybrids in both tables be 

 examined, it will be seen that No. 7 is hybrid in one 

 pair of characters while the other hybrids are hybrid in 

 more, and, because it is pure in certain characters in 

 which Nos. 10 and 12 are hybrid, the progeny of 7 with 

 10 and 12 bear the character in which 7 is pure. If, 

 for instance, hybrids carrying the following materials are 

 mated 



.X X 



.X X . 



.Y Y. 



Y y 



their progeny will all bear the character Y. 



The figures in the first table confirm the inference 

 suggested by the hybrids that grey is dominant to 

 albino ; and, since the greys in the hybrids' progeny are 

 to the albinos in the ratio 3:1, that albino differs from 

 grey in one pair of characters. 



In the previous chapter grey was shown to differ 

 from three other colours each in one pair of characters. 



