NEW COMBINATIONS OF GENES 17 



duced by taking one gene of each pair for each germ cell. In the lower 

 row the three rectangles show three of the great number of diverse 

 combinations producible by union of one germ cell from the father, 

 one from the mother. 



gether half of the genes from each of the two parents. This 

 gives a combination of genes that is different from that of 

 either of the two parents; so that the child will have a differ- 

 ent set of characteristics from either parent. There may thus 

 be produced a combination of genes never before produced, 

 giving an individual with characteristics different from any 

 that have before existed. To this method of operation is due a 

 great deal of the diversity that exists in nature. To it is due 

 at least a certain amount of what we may call evolutionary 

 progress; just how much it is difficult to say in the present 

 state of our knowledge. Examination of some of the rules of 

 this method of producing new combinations will help in 

 grasping it. 



The great rule for the production of a new individual by 

 two parents is this : Each parent gives to the child one member 

 of each of his own pairs of genes. This is indicated in the 

 diagram of Figure 3. If the parent has a thousand pairs of 

 genes, he gives to each child one member of each; a thousand 

 single genes in all. The other parent gives also one member 

 of each of his thousand pairs, so that the child gets again from 

 both together a thousand pairs. 



Each parent may give to the child either member of any of 

 his pairs of genes. We may designate the two members of any 

 of the parent's pairs as maternal (M) or paternal (P), accord- 

 ing as they have come to him from his mother or his father. 

 The child may get then either the maternal gene or the 

 paternal gene. Frequently, perhaps usually, these two mem- 

 bers of the pair are different in their effects. Commonly one 



