188 



GENETICS 



above the normal ear-length found in short-eared rab- 

 bits, that is, 



220 mm. 100 mm. 



= 20 mm. 

 6 



When according to this computation a lop (20 

 mm. X 6 + 100 mm. = 220 mm.) and a pure short- 

 eared rabbit (20 mm. X + 100 mm. = 100 mm.) 

 are crossed, if imperfect dominance occurs, which is a 

 very common phenomenon, it is true that the offspring 

 might present a "blended" appearance. If now these 

 cross-breds of the first generation prove to be tri- 

 hybrids with respect to excess ear-length, there would 

 be sixty-four possibilities in their progeny segregating 

 out just as in the red-kerneled wheat. 



These possibilities would be arranged in the fol- 

 lowing frequencies: 



Since the average litter among rabbits is about five, 

 the chances that these five rabbits will breed true to 

 their hybrid parents and form a perfect blend between 

 their grandparents is 20 out of 64, while the chance 

 of their being like either grandparent is only one out 

 of 64. 



