CHAPTER IX 



THE GAMETOPHYTE IN INHERITANCE 



Thus far the discussions have dealt with inheritance in sporo- 

 phytes; in fact, genetics practically never considers ganietophytes, 

 through which inheritance must pass from one sporophyte to the 

 next. The reasons for this neglect are obvious. Practically all 

 of our land vegetation is made up of sporophytes, and therefore 

 practically all of our experimental material has been sporophytes. 

 Furthermore, gametophytes are inconspicuous (out of sight in 

 seed plants), hard to get at, hard to work with, and apparently of 

 no economic importance. Besides, in animals, as is well known, 

 the generation equivalent to the gametophyte of plants is repre- 

 sented by only a few cell divisions in the maturation of gametes. 

 In other words, the gametophyte has no significance as a discrete 

 generation in the animal kingdom; and since inheritance in plants 

 is of interest to the public chiefly because it throws some light upon 

 inheritance in animals, there has been little demand for any knowl- 

 edge of inheritance in gametophytes. 



It is not surprising, therefore, that very little study has been 

 made of the gametophyte generation in inheritance. There are 

 reasons for believing, however, that such a study might be very 

 profitable. The gametophyte generation, with its haploid chromo- 

 some number, would provide an interesting and critical test of the 

 Mendehan mechanism of inheritance. Certain features of inherit- 

 ance would be expected to differ radically from inheritance in 

 sporophytes. A generalized example might be considered. 



Gametophyte Ab is characterized by exhibiting the A character 

 but not the B. The reverse is true of gametophyte aB. A cross 

 between the two would produce zygote AaBb, followed by a sporo- 

 phyte of the same formula. The following gametophyte genera- 

 tion would contain four types in equal numbers, AB, Ab, aB, and 

 ab. This is the program that would have to be followed if the 

 Mendelian mechanism were at play. One would expect, there- 



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