102 



MENDELISM 



CHAP. 



cells contain 1 2 chromosomes, the gametes will 

 contain only 6. But the 6 chromosomes found in 

 the gamete, whether egg or sperm, are representatives 

 of each of the six pairs found in the body cells. 

 When two gametes unite, each of the 6 chromosomes 

 again finds its mate, and the condition of six pairs is 

 again restored in the body cells of the new individual. 

 Some years ago it was discovered in America 

 that in certain insects the number of chromosomes 





::o-:-' 



• • 



Gametes •/^« 

 of Female •^(/^» 

 (ova) 



Gametes 

 of Male 

 (sperms) 



:%:, 6 



• • 



• ••• 



Fig, 29. 



Diagram illustrating the behaviour of the chromosomes in Proienor. The sex 

 chromosomes are represented as unshaded. The remaining six pairs actually 

 differ somewhat in size, but this is not indicated in the diagram. 



differs in the two sexes. In the bug Protenor, for 

 instance, there are 14 in the female, but only 13 in 

 the male. The odd number in the male is due to 

 the fact that one of the chromosomes is impaired. 

 The female contains 7 pairs ; the male 6 pairs and 

 an odd one. The odd chromosome in the latter sex 

 corresponds to a definite pair in the female. When 

 the female forms gametes the number of chromo- 

 somes is halved, and every egg comes to contain a 



