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THE POPULAR SCIENCE MONTHLY 



"When both gametes carry similar positive factors the zygote has a 

 "double dose" of such factors and is said to be duplex; when only one 

 of the gametes carries such a factor the zygote has a " single dose " and 

 is simplex, when neither gamete carries a positive factor or factors, the 

 zygote receives only negative factors and is said to be nulliplex. Thus 

 the union of gametes AB ($) and AB (J 1 ) yields zygote AABB, which 

 is duplex in constitution; gametes Ab ($) and aB (.J 1 ) yield zygote 

 AaBb, which is simplex; gametes ab ($) and ab (■$) yield zygote aabb, 

 which is nulliplex. 



In some instances a character comes to full expression only when it 

 is derived from both parents, that is, when it is duplex ; if derived from 

 one parent only, that is, if simplex, it is diluted in appearance and is 

 intermediate between the two parents. For example, when white- 



Fig. 5G. Results of Crossing White-flowered and Red-flowered Races of 

 Mirdbilia Jalapa (Four O'clocks), giving a pink hybrid in Fi, which when inbred 

 gives in F 2 1 white, 2 pink, 1 red. (From Morgan, after Correns.) 



flowered four o'clocks which are nulliplex are crossed with red-flowered 

 ones which are duplex the progeny, which are simplex, bear pink 

 flowers; in this case red flowers are produced only when the factor for 

 red is derived from both parents, pink flowers when it is derived from 

 one parent, white flowers when it is derived from neither parent 

 (Fig. 56). 



5. Summary of Mendelian Principles. — Since the rediscovery in 

 1900 of Mendel's work many investigators have carried out similar 

 experiments on many species of animals and plants and have greatly 

 extended our knowledge of the principles of inheritance discovered by 

 Mendel, but in the main Mendel's conclusions have been confirmed 



