444 ELEMENTARY BIOLOGY 



Most people have the impression that where individuals with 

 differing characters are mated, the offspring will show characters 

 somewhere between the characters of the parents. The reason 

 for this common belief lies in the fact that in our everyday 

 experience we notice that children resemble both parents ; but 

 most of us have not taken the trouble to notice further that 

 this resemblance to both parents does not consist o having 

 every character halfway between the corresponding characters 

 of the parents, but in having some characters just like those of 

 the mother and other characters just like those of the father. 



470. The Law of Dominance. Mendel found that this com- 

 plete resemblance of the offspring to one of the parents (in 

 regard to a particular character) was quite the rule with each 

 of the other pairs of characters. Thus, the offspring of a tall- 

 and-short cross were all tall. The offspring of a smooth-and- 

 wrinkled-seeded cross were all smooth, and so on. This fact 

 Mendel called the Law of Dominance. His idea was that 

 where two characters of a pair meet in an individual, one of 

 them dominates over the other. Of a pair of characters, that 

 one which did not show in the offspring is called the reces- 

 sive. It is not destroyed, as we shall see. Of course, he could 

 not tell which of the two characters in a pair would reappear 

 in the offspring before trying them out. In the tables on page 



445 are given the dominants and their alternatives for a num- 

 ber of characters selected from among plants and animals. 



471. The Law of Segregation. The yellow seeds of the 

 hybrid 1 pea plant cannot be distinguished from the pure yellow 

 seeds of one parent. With plants grown from the hybrid yellow 

 seeds Mendel brought about three classes of cross-pollenation. 



1 The word hybrid was formerly applied to the offspring of two parents of 

 different species or races, as, for example, the mule, or a mulatto, or the off- 

 spring of a Caucasian and an Indian. It is now used quite generally among 

 biologists, horticulturists, animal breeders, etc. to mean the offspring of two 

 parents that differ with respect to any particular character. For example, a 

 seedsman might speak of a hybrid tomato, meaning a plant resulting from 

 a cross between two varieties of tomatoes, and so on. 



