400 



ANIM.\L BREEDING 



by the animal breeder when selecting for certain desired 

 combinations of characters not to include also lethal 

 genes or others which unduly diminish the fertility or 

 stamina of the race. There is actual record of a superior 

 race of cattle which perished for this reason. 



Inheritance of Winter Egg Production by Fowls. 

 — It has been found that the ability to produce many 



Fig. 117.1. — Inheritance of a recessive pattern of white spotting 

 seen in "hooded" rats. The parents at the left are a homozygous 

 hooded mother and a heterozygous "Irish" father (black with white 

 belly). An entire litter of their young is shown at the right. Four 

 are homozygous hooded like the mother, five are heterozygous like 

 the father. Note fluctuations in both classes. Such fluctuations are 

 found to be in part heritable. 



Castle, Heredity and Eugenics. Harvard Press. 



Fio. 117 /i. — A Graded Series of Patterns Used in (Jrading the 

 Coats in a selection experiment. By continual selection of the prog- 

 eny of the offspring of the cross shown above, any of these types 

 of patterns can be produced. This result is now supposed to be due 

 to the modification of the eflFects of one main factor for "hooding" 

 by numerous other factors which have the effect of modifying the 

 extent of the white and colored areas. 



Castle. 



