290 THE CONTINUITY OF THE RACE 



constantly increasing interest in cytological studies had led to the recogni- 

 tion of a number of fundamental and universal cell phenomena, particu- 

 larly mitosis, maturation (meiosis), and the details of fertilization. 



The Sutton-Boveri hypothesis. The American cytologist W. S. Sutton, 

 who was investigating the details of maturation, had, like nearly all other 

 workers in biology, become greatly interested in the newly discovered 

 "Mendelian heredity." About 1902, he realized that there was a striking 

 parallel between Mendel's laws and certain details of maturation and 

 fertilization. He saw that if we but conceive of the Mendelian factors or 

 genes as being located in the chromosomes, then the latter provide a 

 vehicle and a precise mechanism that will account for: 



1. Segregation of the factors at gamete formation (gametic purity). 



2. Recombination of the factors at fertilization (zygote formation). 

 And, if we can assume that the paired chromosomes at the metaphase 



of the first meiotic division (page 219) may have their paternal and mater- 

 nal elements at random on either side of the equatorial plate of the spindle, 

 then maturation will also provide a perfect mechanism to account for: 



3. The independent assortment of as many pairs of factors as there are 

 pairs of chromosomes, so long as each pair of allelomorphic factors is in a 

 separate pair of chromosomes. 



Sutton's reasoning was based upon the striking parallels between 

 the phenomena of Mendelian inheritance and those shown by the chromo- 

 somes at meiosis. Another supporting fact cited by Sutton was the ap- 

 parent lack of influence of cytoplasm upon inheritance. We have seen 

 that it makes no difference which parent is tall or which is dwarf; in 

 either case, the Fi will be tall, and the F 2 will show a ratio of 3 tails and 1 

 dwarf. We also know that the only thing the male and female parents 

 contribute equally to the zygote is their chromosome complex. All or 

 nearly all the cytoplasm comes from the female parent, yet the male 

 parent appears to contribute equally with the female to the hereditary 

 qualities of the offspring. 



Sutton's hypothesis, which came to be known as the Sutton-Boveri 

 hypothesis (after Sutton and Theodore Boveri, the latter a cytologist 

 who contributed much to our knowledge of maturation), at first met with 

 much opposition, but gradually, more and more evidence accumulated 

 to support it, until by 1920 to 1925 it was accepted as a proved principle 

 in biology. 



SEX DETERMINATION AND SEX LINKAGE 



Shortly after the announcement of the Sutton-Boveri hypothesis, 

 further studies on cytology brought to light still other parallels between 

 chromosomes and certain peculiar modes of inheritance that did not 



