MATURATION PHENOMENA OF GERM CELLS. 155 



tation is explanatory of the kind of phenomena that we have 

 discussed. 



5. CHROMOSOMAL COMBINATIONS AND THE MENDELIAN RATIO. 

 In his paper on " The Chromosomes in Heredity " ' Sutton 



4 



argues that the combination of paternal and maternal chromo- 

 somes in the fertilized egg would result in a Mendelian ratio. It 

 will be recalled that Mendel 2 in his experiments on crossing 

 varieties of Pisuin, to determine the law of transmission o 

 parental characters to the hybrid, found the crosses to result in 

 the ratio I D:2 Dr : i r, in which D represents the pure char- 

 acter of one parent, r the pure character of the other parent, and 

 Dr represents the possession of both characters. In other 

 words : out of four offspring resulting from such a cross, one 

 would resemble the father, one the mother, and two combine the 

 characters of both parents. 



Sutton starts with the fact that there are two series of chro- 

 mosomes in each fertilized egg, A, B, C, ... ;/ and a, b, c, ... 

 n, the first set of paternal origin (from the spermatozoon) and the 

 second of maternal (from the ovotid). In these series A is the 

 homologue of a, B of b, and so on. In the synapsis stage of the 

 germ cells A would conjugate with a, B with b, and so on, so 

 there would be formed the bivalent chromosomes Aa, Bb, Cc, 

 ... n. In the reduction division A and a would pass to sep- 

 arate cells, and such would be the case with B and b and the re- 

 maining paired chromosomes. 



Then Sutton takes the case where there are the two homol- 

 ogous chromosomes A and a in an ovogonium and A and a in a 

 spermatogonium ; in the maturation period there would be 

 formed Aa in the ovocyte, and Aa in the spermatocyte ; the 

 ovotids would contain then either A or a, and the spermatids 

 either A or a. There would then result in fertilization these 

 combinations : 



A $ + A 9 = AA 



A $ + a 9 = Aa 



a $ + A 9 = a A 



a $ -\- a 9 = aa. 



1 BIOLOG. BULL., 4, 1903. 



~ 2 " Versuche iiber Pflanzenhyhriden," Vfrh. nat. \ r er. Briinn, 4, 1865. 



