596 



Journal of Agricultural Research 



Vol. XX, No. 8 



promising for further genetic investigation, six F x sows were purchased 

 in June, 1916. 



The six sows, numbered 1 to 6 in Tables I and II, were bred back to a 

 Duroc- Jersey boar, since this type was recessive in a number of charac- 

 ters in the original cross. Each female, except 9 5, gave at least one 

 litter, and $ 3 gave two litters. A total of 42 F 2 offspring by this back- 

 cross was thus obtained. The original mule-foot P x parent was without 

 doubt homozygous in mule-foot and black and probably had the genetic 

 formula BBMM, where B is a factor for black and M is a factor for mule- 

 foot. The Duroc-Jerseys had the genetic formula bbmm, where b 

 stands for red, and m for cloven-foot. The F x hybrids were then heterozy- 

 gous in both black and mule-foot (BbMm) and, if the case is one of simple 

 Mendel ism, produced gametes BM + Bm + bM + bm with equal fre- 

 quency. Mating the F x females to the Duroc-Jersey male should give in 

 Mendelian terms: 



BM + 

 bm + 



Bm + 



bm 



bM+ bm 



BbMm 4- Bbmm + bbMm 4- bbmm 

 black black red red 



mule-foot cloven mule-foot cloven 



F x gametes 

 Duroc-Jersey gametes 

 F 2 zygotes 



That is, the F 2 classes would be of four equally frequent types. The 

 calculated and observed results agree, for there were produced 8 black 

 mule-foot, 11 black cloven-foot, 9 red mule-foot, and 14 red cloven-foot 

 where 10.5 of each kind is the calculated result. (See Pi. 70.) So far 

 as the evidence goes, the allelomorphic pair of factors for syndactylism 

 and cloven-foot is quite independent of the allelomorphic pair for black 

 and red. The ultimate recessive segregates, red cloven, bred true when 

 mated inter se and gave 30 red cloven in the F 3 and F 4 generations. 



Table I. — Distribution of F 2 segregates from mule-footX. Duroc- J 'ersey F, hybrids mated 



back to Duroc-Jersey 



