316 



CHARACTER OF OFFSPRING 



When peas are rolled down an inclined plane through a 

 small opening against nails, they line up in pens in a very 

 definite order. When this experiment is performed, a 

 sorting out, known as a normal distribution, occurs. Few 

 peas are found in the end pens, many in the center. This 

 illustrates the law of chance, discussed on p. 317. 



from each other. Some are tall and some are short, some are 

 blue-eyed and some are brown-eyed. This will be explained later. 



We have learned that 

 a process called matura- 

 tion or ripening occurs 

 in the development of 

 mature germ cells in the 

 parent organism. This 

 maturation of the germ 

 cells accounts for the 

 differences among off- 

 spring. Chromosomes 

 are thought to possess 

 combinations of char- 

 acter-determiners called 

 genes. These genes are 

 found to be in pairs in the primary sex cells. During the matu- 

 ration process, reduction takes place. In reduction, one member 

 of each pair goes to a given germ cell. Consequently, each germ 

 cell has one half the number of chromosomes found in the pri- 

 mary sex cell. If the primary sex cell had a pair of character- 

 determiners for eye color, one of this pair carries blue and the 

 other brown, the chromosome containing the gene for blue eyes 

 would go to one germ cell and the chromosome containing the 

 gene for brown eyes would go to another germ cell. A primary 

 sex cell may have two characters for a particular trait, but a germ 

 cell only has one and is pure in regard to any particular trait. 

 Consequently, the same organism may produce germ cells with 

 unlike characters. The sperm cells of the male are not identical ; 

 eggs, too, have different character-determiners or genes in them. 

 When the sperm and egg meet in the process of fertilization, the 

 characters of the fertilized egg depend upon the characters in the 

 genes in the combined chromosomes of both the sperm and egg. 



