OPERATION OF THE GENETIC SYSTEM ^-J 



than the other, certain unfavorable conditions might injure 

 or destroy one type and not the other. As a result, all or 

 most of the eggs would be fertilized by the uninjured type 

 of sperms. Then all (or most) would produce individuals 

 of the same sex. If the sperms with X were the ones injured, 

 then all the offspring would be males; in the alternative 

 case, all the offspring would be females. 



Such effects might be produced by conditions of tempera- 

 ture, or chemical conditions, or by certain elements in the 

 food of the parent. It would then be found experimentally 

 that these conditions "determine sex." Whether such effects 

 are actually produced is to be discovered only by observa- 

 tion and experiment. 



(d) The eggs might have such chemical or physical 

 properties as to admit one of the kinds of sperm, not the 

 other. This would determine what sex is produced. There 

 are indications that something of this sort occurs in some 

 organisms. 



(e) Certain chemical or physical conditions of the en- 

 vironment might alter the properties of the egg, making it 

 admit one type of sperm, not the other. Such environmental 

 conditions would then determine the sex to be produced. 



2. Destruction or division of an X-chromosome. — Any- 

 thing that would destroy one of the X-chromosomes in a 

 fertilized egg containing two X's would determine the sex: 

 the individual produced would be a male instead of a fe- 

 male. 



There is strong evidence that such transformation of an 

 individual that began as a female into a male (wholly or 

 partly) occurs at times. There occur in insects individuals 

 in which one-half of the body is female, the other half male. 

 In some animals it is easy to detect this, because the males 

 and females differ in structure or color in all parts of the 

 body. Such individuals are known as gynandromorphs. In 



