PROBLEM I. Why Offspring Resemble Their Farents 



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461 



Fig. 407 Reduction division of a jnale pri??iary 

 sex cell. How ?/hviy pairs of cJ?roinosoiiies are 

 there? Hoiv many chromosomes? How many 

 chromosomes in each daughter cell? Does a 

 daughter cell have any chromosomes in pairs? 





Fig. 



1 2 3 



408 Reduction division of a female pri- 



mary sex cell. How many chromosomes in the 

 pri?nary sex cell? In each daughter cell? Com- 

 pare the chromosomes in male and fejnale re- 

 duction division. 



Fig. 409 Except for the egg cells the mother hippopotaynus produces, all the cells ifz 

 the mother have the sojne number and kinds of chro7nosomes. How are the eggs 

 different? The cells of the child formed from a fertilized egg will have the same 

 chromosome number as the cells of each parent. Why? (national zoological park) 



Try Exercise 5 to review the three steps 

 in maturation of sperms. 



In females, when the primary sex cell 

 goes through reduction division, produc- 

 ing the haploid nuclei, the cytoplasm 

 divides unequally. Thus one daughter 

 cell is large, the other small. In the mi- 

 totic division that follows, the large 

 daughter cell again divides unequally. In 

 this way, of the four cells that are pro- 

 duced by these two divisions, one is large 

 and three are tiny. Only one cell sur- 



vives, the large one. This becomes the 

 egg. It, like the sperm, has onlv one of 

 each pair of chromosomes and only a 

 single set of genes because of the reduc- 

 tion division. In some animals large 

 amounts of food material, called yolk, 

 accumulate in the egg cell, making it 

 very large. Fish and frog eggs, and, par- 

 ticularly, bird eggs are good examples of 

 this. 



Fertilization and chromosome number. 

 You have just read how the sperm and 



