164 General Biology 



breeding there may be among plants or animals, there are only two types 

 of offspring produced, i. e., pure stock and half-breeds. 1 The eggs and 

 sperm in the germ-plasm always remain pure. That is, if a white and 

 black animal mate, a portion of the eggs in the ovary of any female off- 

 spring from such union will be carriers of pure black, and a portion will 

 be carriers of pure white characteristics. The sperm of the male, like- 

 wise, are carriers of one or the other colors, but are not themselves half- 

 breed. It will be noticed, therefore, that from this Mendelian theory 

 additional evidence is brought forth to substantiate the Weismannian 

 theory of germ-plasm, which holds that the germ-plasm is separate and 

 distinct from the rest of the body. 



The color of the skin of any offspring of black and white animals 

 may be of any shade, from pure black, to almost, or entirely white. But 

 the sperm and the egg have not intermingled in so far as color is con- 

 cerned. The color shows up on the outer part of the body, or in what 

 we call the somatoplasm. The germ-plasm always remains pure, so that 

 in the next succeeding generation, if any of these half-breeds in turn 

 mate with each other, we have the four possibilities of a sperm carrying 

 the genes for whiteness meeting with an tgg carrying the genes of black- 

 ness and again producing a half-breed, or a sperm carrying genes of 

 blackness meeting with an tgg carrying genes of blackness and pro- 

 ducing a pure black, while a sperm carrying the genes of blackness 

 mating with an egg carrying the genes of whiteness, produces a half- 

 breed, and a sperm carrying genes of whiteness with an Qgg carrying 

 genes of whiteness produces a pure white. 



From observation, however, it is found that most half-breeds will 

 look like one or the other of their parents in so far as color of skin, eyes, 

 and hair is concerned. Whatever color the offspring shows, is known 

 as the dominant color. 2 We cannot tell, however, until we observe the 

 first brood of half-breeds which is the dominant color. 



We do not know why one characteristic is thus dominant, but the 

 important thing to remember is that this entire possibility of any of 

 the four possible matings mentioned above taking place in any mixed 

 offspring, is all a matter of chance. Having observed thousands of in- 

 stances of this kind among both plants and animals, scientific men now 

 accept it as a fact that we do obtain two individuals of pure stock, and 

 two half-breeds from matings of mixed ancestry. It will be noticed 



1 This refers to the crossing of two pure breeds, of course. 



^Recessive is the word set in opposition to dominant. A recessive characteristic is always pres- 

 ent in the germ-plasm of an animal or plant of mixed ancestry, but it does not show in the 

 somatoplasm — in any part of the body proper outside the germ-plasm. The dominant character- 

 istics cover up the recessive characteristics. For example, in half-breed offspring'. — a cross between 

 white and black parents — if all these half-breeds are black, we call black the dominant charac- 

 teristic as to color, though such half-breed has just as much white in him as he has black. The 

 white which is present but which is not seen is called the recessive characteristic. 



It is very important, however, to remember that in so far as the germ-plasm — the sex cells 

 themselves, that is, the eggs and sperm — is concerned, each egg and each sperm has, roughly speaking, 

 one-half black and one-half white characteristics ; but the dominant characteristic is the only one 

 which shows, and that only in that part of one's make-up zvhich is not germ-plasm. 



To clarify the matter; if half-breeds, which are the offspring of black and white parents are all 

 black, we call black the dominant color. 



