206 

 mendel's experfments with peas. 



He experimented with garden peas. All progeny from each 

 cross were kept separate for a number of generations. He 

 selected contrasted characters which are alternative. Seeds, 

 round or angular ; pods wrinkled or smooth ; stems tall or 

 dwarfed. Take for example his experiments in crossing peas 

 differing only in color of the cotyledons, viz : yellow and green. 

 All the crosses resulting from yellow vines pollinated from 

 green vines were yellow seeds only- There were found to be 

 no green seeds, and no intermediate ones. This characteristic 

 of the crosses is especially to be noted. Mendel applied the 

 term "dominant" to the tendency of the yellow color to domi- 

 nate over the green color. The green color was suppressed 

 in the first generation of crosses, therefore called this "re- 

 cessive." 



All the seeds were then grown and the plants of the third 

 generation set seeds. It was found that the third generation 

 differed from the second. They were found to be partly yellow 

 and partly green in the proportion of three yellow dominant 

 characters to i green or suppressed color. The actual figures 

 were as follows : 



258 seeds apparently yellow, were produced by crossing yel- 

 low with green varieties. 



258 hybrids when crossed together produced 8023 plants 

 6022 yellow species to 2001 green species or 3 to i. 



In the second generation 519 seeds resulted in 353 yellow 

 and green mixed and 166 yellow. 



The result may be expressed as follows, D representing "domi- 

 nant" and R "recessive" : 



Ovules fertilized by pollen, result in the following progeny com- 

 binations : 



(D + R) X (D -I- R), which is equal to: 



D- -|- 2 D R + R-, which may also be expressed": 



D D + D (R) -f (R) D + R R. 



The recessive or green seeds, R- R. above, wdien bred to- 

 gether will not produce any but green seeds. They breed 

 true. But the dominant seeds or yellow all look alike, (the 

 pure stock D D that when bred together breed yellow, true, 

 and the D (R), (R) D, w^hich L^re apparently yellow, but when 

 bred together do not breed true.) To separate the pure domi- 

 nant stock, yellow, D D in the diagram, it is necessary to test 

 out the hybrids by self-pollinating each of the plants produced 

 from the yellow seeds. The dominant class D' D, or pure yel- 

 low stock, will produce yellow^ seeds alone, while the hybrids 

 D (R), (R) D, apparently yellow, with suppressed green char- 

 acteristics, will again produce yellow^ and green seeds in the 

 proportion of 3 to i. 



