PRINCIPLES OF LIVESTOCK BREEDING. 
'&*&?'+ 
19 
-*j 
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 y 
permits only red to develop. The first cross between a black stock 
(COEE) and a red stock {CCee) is black (COEe). 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 
4L3//VO FROM RED STOCK 
REPRODUCT/VE CELLS 
F/RST CROSS - BLACK 
REPRODUCT/VE CELLS 
4 K/NDS RESUL T/NG /N4X/A/DS, 
OF YOUNG OA/ CROSS W/TH 
ALBINO FROM RED STOCK 
(cceej 
25 PERCENT 
BLACK(CcEe) 
2S PERCENT 
RED (Ccee) 
25 PERCENT 
ALBlHO TRAMS- 
M/TTIHG 
BlACK(f:c£ & ) 
25 PER CENT 
ALB/NO T/iAA/S- 
■M/rr/MG oa/ly 
/?££>(cce<$ 
Fig. 3.— Diagram illustrating inheritance of 2 independent Mendelian 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. 
