PRINCIPLES OF LIVESTOCK BREEDING. 



19 



determine any particular color. It merely cooperates with other 

 factors. One of the other factors, which we may represent by the 

 symbol E, enables black pigment to develop. Its alternative, e, 

 permits only red to develop. The first cross between a black stock 

 (CCEE) and a red stock (CCee) is black (CCEe). Thus black is 

 dominant over red. The first-cross animals produce reproductive 

 cells containing E and e, respectively, in equal numbers. Since 

 factor E and its allelomorph e are wholly independent of factor C 

 and its allelomorphs, it is possible for a guinea pig to have any com- 

 bination of the two sets. Thus an albino may transmit black only 

 (ccEE) or red only (ccee) or both (ccEe). Suppose that an albino 



3LACKX 



4LB/A/0 FROM RED STOCK 



REPRODUCT/VE CELLS 



F/RST CROSS - BLACK 



REPPODUCT/VE CELLS 



4K/ND5 RESULT/NG //V4X/W5) 

 OF YOUNG ON CROSS W/TH 

 ALBINO FROM RED STOCK 

 (ccee) 



25 PERCENT 

 BLACK (CcEe) 



25 PERCENT 

 RED (Ccee) 



25 PER CENT 



ALBIHO TKAHS- 

 MITT/NG 



BLACKCccEe) 

 25 PER CENT 



filSWO T/tAMS- 

 \M/rT/MG OW.Y 



Fig. 3. — Diagramillustratinginheritanceof 2 independent Mendeiian factors. A pure-black strain of guinea 

 pig ( CCEE) is crossed with albinos from red stock (ccee). The young of the first cross are all black but 

 produce four kinds of reproductive cells in equal numbers, as revealed by appropriate crosses. 



of the second type (ccee) is crossed with a black stock which breeds 

 true (CCEE) ; the first cross will be colored (Cc) and the color will be 

 black (Ee). If, now, these crossbred blacks are bred with the same 

 albino stock, we expect half the young to be colored (Cc) and half to 

 be albino (cc). Of the colored young, half should be black (CcEe) 

 and half red (Ccee). The albinos will be divided similarly into two 

 classes, those which transmit black in half their reproductive cells 

 (ccEe) and those which transmit only red (ccee). These two classes, 

 however, will look alike. The cross thus should produce 50 per cent 

 albinos, 25 per cent reds, and 25 per cent blacks, which it actually 

 does. 



