MENDELIAN INHERITANCE IN OENOTHERA PRATINCOLA 3 



Besides its characteristic a or ft part, each gamete carries a group of 

 factors common to both a and ft gametes. The characteristic a and ft 

 portions of the gametes may consist of a single chromosome or of a group 

 of chromosomes, but probably the latter, for very few characters have 

 been found which are not connected with the a or ft portions of the gametes. 

 At reduction, a and ft behave as units; that is, there is no interchange of 

 factors or chromosomes between the characteristic a and ft portions, each 

 passing into the gametes (the a into the female, the ft into the male) just 

 as it entered the zygote from the parent. There is, however, the usual 

 free segregation among the remainder of the chromosomes, each member of 

 the homologous pairs accompanying with equal frequency the a and the ft 

 portions. Thus factors entering a zygote in the characteristic a or ft 

 chromosome (or chromosomes) occur in the a or ft gametes, respectively, 

 which it produces ; but those factors which entered the zygote in the remain- 

 ing, freely segregating group of chromosomes, occur as frequently in the 

 a as in the ft gametes produced. Characters whose factors belong to the 

 a or to the ft portion are inherited matroclinically or patroclinically, respec- 

 tively; those whose factors belong to homologous and freely segregating 

 chromosomes common to both a and ft gametes are inherited in a Men- 

 delian manner. 



Mut. formosa arose from i. typical by modification of a factor for flatness 

 in the a portion of the a gamete, that is, by change of a factor which has no 

 counterpart in the ft portion of the ft gamete. Change being in the a 

 (female) gamete only, inheritance in crosses between mut. formosa and f . 

 typica E is, therefore matroclinic. If mut. formosa is used as the pistillate 

 parent the a gamete received by the progeny is the mutated a of mut. 

 formosa (designated hereafter as <*'), and the progeny is therefore mut. 

 formosa; if f. typica is used as the pistillate parent the a gamete received 

 by the progeny is the normal a gamete of Oenothera pratincola, and the 

 progeny is f . typica. 



Strain C differs from strain E in having, in addition to the factor for 

 flatness in the a portion of the a gamete, a freely segregating (Mendelian) 

 factor for flatness (F) present in both a and ft gametes, of which the reces- 

 sive allelomorph (/) is carried by strain E. Thus the constitution of 

 strain C is aftFF, and the gametes which it produces are aF (female) and 

 ftF (male). The constitution of strain E is aftff, and the gametes which 

 it produces are af (female) and ftf (male). The constitution of mut. 

 formosa is a'ftff, and the gametes which it produces are a'f (female) and 

 ftf (male). Therefore strain C (aftFF) pollinated by mut. formosa (a'ftff) 

 gives a flat-leaved progeny (a&Ff) which breeds true, for the a gamete 



GENETICS 6 : Ja 1921 



