Constitution of the White Leghorn Breed. 201 



It is thus apparent that in the mating under consideration among 

 every 8 birds we may expect to have 4 white and 4 dark. Of the 

 whites, 2 will be d^ d^ and 2 99- Of the darks, one will be black 

 and 3 barred ; the black bird and one of the barred birds will be 9 9 . 

 It appears that the expectation of producing a c^ homozygous for 

 barring would here be attained. One out of every 8 birds (or one 

 among every 3 barred cf &) should be homozygous for B. 



We may now compare with these theoretical data the results 

 obtained in the actual cross. As shown in Table 13 (p. 177), among 

 50 birds, 25 were white and 25 dark. Of the darks, 13 were black 

 and 12 were barred. According to expectation we should have among 

 48 progeny the same proportion of light and dark birds, but the barred 

 should stand in proportion to the blacks as 18 to 6; and all the blacks 

 should be 9 9 . It is at once apparent that these expectations are 

 b}^ no means fulfilled, and we may therefore turn to a consideration 

 of the second possible interpretation involving a different zygotic 

 constitution for 9 325E. 



Second Instance. — (^ 32oB (barred) X 9 32oE {white); second 

 possibility: On p. 177 reference has been made to the fact that 9 

 325E, so far as appearance was concerned, might have been hetero- 

 zygous for the barring factor or might lack it. In the previous in- 

 stance the case has been considered in which the bird was assumed 

 to be heterozj^gous for B. In the present instance we may consider 

 the probable results of mating in case 325E lacked this factor but 

 was heterozygous for 7, — in other words, possessed the zygotic con- 

 stitution C'2!b2FfIi. The cT 325B would form gametes as previously 

 shown while the 9 might be assumed to form gametes 



CbFI • CbFi • Cbfl : Cbfi 



The mating would then be represented : 



9 CbFI ' CbFi - Cbfl ■ Cbfi X 

 d^ CBfi 'Cbfi = 



^d" 



C2b2f2li, white 

 C2Bbf2li, white 

 I C2Bbf2i2, barred 

 I C2&2/2^2, black 



