MIRACLES' OF SCIENCE 



ity on the breeding of a better human race should 

 understand the essentials of what may be called the 

 Mendelian formula. An illustration drawn from the 

 animal world will present this perhaps more vividly 

 than the case of the peas. If a black guinea pig of 

 a pure black strain is mated with a white guinea pig, 

 as in Professor Castle's experiment, all the offspring 

 will be black. This shows that black and white, as 

 applied to the hair of the guinea pig, are unit char- 

 acters, and that the black color is dominant. But 

 if these black guinea pigs of the second generation 

 are allowed to inter-breed, three out of four of the 

 offspring will be black, and the fourth will be pure 

 white. Further breeding experiments will show that 

 of the three black guinea pigs of this third genera- 

 tion, one is pure black, and will have offspring only 

 of its own color; whereas the other two are "mixed 

 dominants," and will have one in four of their 

 progeny pure white. 



If we were to label the four guinea pigs of the third 

 generation A, B, C, and D (A, B, and C, being black, 

 and D white) we shall state the Mendelian formula in 

 its simplest aspect if we say that A is a pure domi- 

 nant, and will have nothing but black descendants; 

 and that D is a pure recessive and will have nothing 

 but white descendants; whereas B and C are mixed 

 dominants and will have descendants that will dupli- 

 cate the A, B, C, and D formula over and over. 



A clear understanding of this simple formula gives 

 an explanation of many observed facts of heredity 

 that were formerly mysterious. For example, Profes- 

 sor Punnett was able to explain anomalies in the 



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