462 Organ'mns Are Products of Heredity and Eiiviroimient unit ix 



^^^ develop with the half number of somes and sets of genes in pairs, and the 



chromosomes, one of each original pair. species number remains constant from 



When the sperm and egg unite in fer- one generation to another. More impor- 



tilization the fertilized t^^ gets a half tant still, the fertilized egg, and every 



set of chromosomes from the sperm and cell that forms from it by mitosis, has the 



a half set from the t^2^. Together they full or double set of genes. To review 



make the full diploid number. Thus, the w hat you have just read, Exercise 6 will 



fertilized e^^ will again have chromo- be helpful. 



Questions 



1. What are the two distinct types of cells in complex animals? What 

 are germ plasm and somatoplasm? 



2. Why do oifspring look like their parents? 



3. Which part of the cell is of great importance in heredity? 



4. What is the gene theory? With whose name is it associated? 



5. Describe chromosomes as to shape, origin, and composition. What 

 position are genes supposed to occupy in a chromosome? Describe 

 what happens to the chromosomes from the time the nuclear mem- 

 brane disappears until two nuclei are formed. What is this complex 

 division of the nucleus called? 



6. What mitotic structures may be found in stained cells? 



7. Why does every cell of a cat normally have the same full set of 

 chromosomes and genes possessed by the fertilized tgg cell? What 

 seems to determine that a cell grows into a muscle cell or an eye cell? 

 What interesting facts about chromosome number does the tabic 

 show? 



8. Why does fertilization not double the number of chromosomes in 

 each generation? Define haploid and diploid. 



9. What is meant by maturation? Which cells go through maturation? 

 Describe the reduction division which occurs during maturation. In 

 what minor respect does maturation in the female differ from that in 

 the male? 



10. In what process does the haploid number become diploid? 



1 1. Write the letters A to K on a sheet of paper and opposite them write 

 the corresponding words missing from the account that follows: 

 Somatoplasm forms A cells. Germ plasm forms cells called B. Chroma- 

 tin is supposed to contain C which produce the various D of the or- 

 ganism. All the cells of a higher organism (with one exception) have 

 a complicated nuclear division called E. As a chromosome splits 

 lengthwise each half gets a F of genes. After a mitotic division the 

 number of chromosomes in each daughter cell is the G as in the mother 

 cell; the number and the kind of genes are the H. Every cell develop- 

 ing from a fertilized cat t^^ cell will have / genes. In reduction divi- 



