FERTILITY 213 



The peculiarity about this discovery is that the 

 second factor, L2, is sex-linked, which means in this case 

 that it is carried by the eggs that will produce the males 

 in the next generation, and not by the eggs that will 

 produce the daughters. Hence if the daughters of high- 

 producing hens are selected, one does not get in them 



iaiieriraace of fcrUWfy irifovvL (fa\r\) 



Low9 F. L, L, fUz — Lc Low? 



iXcrodl 1 1 ij (z — U (X^r^cS 



X«^ro9 

 {Loy^cS 



T-t/jj^ Lew 9 -^x-i^ (Lcwp 



Fig. 102. — Illustrating Pearl's hypothesis. F = female factor present 

 in half of the eggs and determining sex. Li = factor for low egg produc- 

 tion; U, its allelomorph for zero production of winter eggs. L2 = factor 

 for high winter production; U, its allelomorph. 



the high productiveness of the mother. It is her sons 

 that inherit the character, although they cannot show 

 it except in their offspring. 



. Aside from whatever practical interest these results 

 may have, the facts are important in showing that such 

 a thing as a factor for fertility itself may be present, 

 without otherwise being apparent, and that this factor 



