SYNAPSIS 



Heredity - 479 



TELOPHASE OF LAST GONIAL 

 DIVISION SHOWING DIPLOID 

 NUMBER OF CHROMOSOMES 



INTERMITOTIC STAGE 

 OF EARLY AUXOCYTE 



PROPHASE STAGE SHOWING 



CHROMOSOMES, BEGINNING TO 



PAIR 



1st MEIOTIC DIVISION 



2nd MEIOTIC 



FOUR HAPLOID GAMETES 



Fig. 26-4. Diagram of meiosis in a cell possessing three pairs of chromosomes. 



equipped to develop into an embryo, but 

 the polar bodies are not. 



The behavior of the chromosomes during 

 the maturation of the eggs is precisely the 

 same as it is during the maturation of the 

 sperm (Fig. 26-4). Consequently the net re- 

 sult of oogenesis is the production of four 

 haploid cells, but only one of these can func- 

 tion as the female gamete. When fertilization 

 occurs, this ripened egg transmits its haploid 

 set of chromosomes to the nucleus of the 



zygote, and this is the essential donation of 

 the female parent to the genetic constitution 

 of the offspring. 



Free Assortment of Chromosomes during 

 Meiosis. As was emphasized previously (p. 

 51), the fact that only one division of the 

 chromosomes occurs during the two meiotic 

 divisions results inevitably in a reduction of 

 the chromosome number of the gametes as 

 compared to the other cells of the animal. At 

 one point or another during meiosis the 



:*..» 



Fig. 26-5. Second polar body forming 

 at the surface of the maturing egg of 

 the whitefish. This photograph shows 

 the telophase of the second meiotic 

 division. Note that the polar body 

 (above) receives a full (haploid) set of 

 chromosomes, but only a very small 

 fraction of the cytoplasm. Most of the 

 cytoplasm is retained by the ripe egg 

 cell. (Copyright, General Biological Sup- 

 ply House, Inc.) 



