MENDEL'S LAWS OF HERIDITY 385 



dividuals of the same brood differ among themselves and from 

 their parents they still resemble their parents, and hence each 

 other, more than they do distant relatives or unrelated members 

 of the same species. That is to say, the peculiarities of the 

 parents tend to reappear in the offspring. This, in some cases, 

 has been found to be controlled by very simple laws, known as 

 Mendel's Laws of Heredity. If the two parents differ with 

 regard to a certain character the offspring of the first generation 

 will inherit equally from both parents. In the second genera- 

 tion one-fourth will have the original paternal character only, 

 one-fourth will have the original maternal character only, and 

 the remaining two-fourths will still be mixed like the first gen- 

 eration. In the third generation the mixed two-fourths of the 

 preceding generation will be divided into a fourth pure paternal, 

 a fourth pure maternal, and two-fourths mixed. In the fourth, 

 fifth, etc., generations this process will continue. In this it 

 must be recognized that a character may be present, though not 

 evident. Such a character is said to be recessive while the op- 

 posed character, which is evident, is said to be dominant. To 

 illustrate we may take a simple case. If the red and white 

 varieties of Mirabilis Jalapa (four o'clock) are crossed, the off- 

 spring in the first generation are all pink. The second genera- 

 tion (secured by close fertilization of the pink generation), 

 however, consists of three kinds, viz.: One-fourth white, two- 

 fourths pink, and one-fourth red. The white and red forms 

 are said to be pure because they continue to produce only white 

 and red, respectively, in succeeding generations if close fertil- 

 ized. The other two-fourths of pink flowers in the next 

 generation again break up into white, pink, and red forms in 

 the proportion of 1:2:1, as before, and thus the pink or mixed 

 forms continue in each generation to separate into the three 

 kinds. 



783. When the two parental characters are not equally 

 potent, i. e., when one is dominant, the other recessive, the 

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