12 GENETICS 



be formed, and by restoring the usual number by union of 

 two pieces? This must all mean something. What does it 

 mean? 



In trying to answer that question, the investigators re- 

 flected on certain facts. First, these chromosomes are found 

 in the eggs and the sperm, which unite to form a new indi- 

 vidual, a new person. Second, these germ cells are the only 

 connection that exists between parent and offspring; they 

 are all there is that comes from the parents. Yet the child 

 produced from their union is in many details like the par- 

 ents. This likeness must be brought about by the minute 

 germ cells that unite to form the fertilized egg. Such like- 

 ness to parents may show itself in respect to a very great 

 number of different characteristics — in respect to form of 

 the different features, colors, size, physiological peculiari- 

 ties, and the like. This seems to require that this minute bit 

 of material, the fertilized egg, should be very complex. 

 And very complex it is found to be, in the matter of these 

 chromosomes. 



Are the Chromosomes the "Material of Heredity"? — 

 And so the idea came to investigators that perhaps this 

 complex apparatus of chromosomes is what brings about 

 the likeness of children to parents. This likeness of parent 

 and offspring is one of the manifestations of heredity; it 

 was formerly considered that heredity consisted only in 

 such likeness. So the early investigators said: Perhaps the 

 chromosomes are the "materials of heredity." This would 

 account for the exactness of their behavior, the precision 

 with which they divide, and the accuracy of their distribu- 

 tion in the body. 



But how can it be discovered whether this interesting 

 idea is a true one? How can it be determined whether it 

 is indeed this apparatus of chromosomes that brings about 

 likeness to parents, that brings about heredity? 



Proposed Tests. — The only chance for doing that is to 



