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THE AMERICAN NATURALIST [Vol. XLVli 



Chromosomes in Relation to Mendelian Factors and 

 a Physical Basis of Inheritance 

 Suppose we maintain the factor for the abnormal con- 

 dition to be a particle of one chromosome. G-ametes of 

 the abnormal strain all contain the factor for abnormal- 

 ness, as reciprocal crosses with the normal give the same 

 results. In a cross a pollen grain of the abnormal strain 

 unites with an egg of normal (402) parentage, and an 

 intermediate is produced in F^ The chromosome con- 

 taining the factor for abnormalness is partly neutralized 

 by pairing with a normal homologue. Gametes of two 

 kinds are formed in approximately equal numbers in F l7 

 those containing the factor for abnormalness and those 

 without it. But on a chromosome hypothesis, how are 

 these gametes formed? There are two reduction di- 

 visions and 48 chromosomes, 24 of abnormal parentage 

 and 24 of normal. According to current cytological in- 

 vestigation and interpretation, each chromosome sepa- 

 rates from its homologue in its entirety during the first 

 reduction division, so that, eventually, two kinds of 

 gametes are formed as regards chromosomes. The fac- 

 tor for abnormalness or fasciation is in one chromosome, 

 and chromosomes are believed to be in homologous pairs 

 —one maternal with one paternal. The chromosomes of a 

 homologous pair separate during the heterotypic ana- 

 phase, one going to each pole, it being contrary to current 

 interpretation to believe that both members of a pair may 

 go to the same pole. On this basis, according to the law 

 of chance, approximately half the nuclei at the end of the 

 heterotypic division will contain the chromosome carry- 

 ing the factor for abnormalness and from half it will be 

 absent. 



Experimentally it has been shown that we have been 

 dealing with only one pair of unit characters and that no 

 complications are present. The various crosses have al- 

 ways given uniform results in F 1? even between species, 

 and the fertile cross has given a close 1:2:1 ratio in F 2 . 

 Logically, then, one is led to believe that one out of the 



