PLANT BKEEDING AND EVOLUTION 



189 



In this instance, however, Mendel crossed peas which bore 

 smooth yellow seeds (F) with peas having wrinkled green 

 seeds (wg)* The 

 large letters (SY} 



PARENTS 



(Fig. 99) show that 

 these characters were 

 dominant in the off- 

 spring, wherever they 

 occurred, and the 

 small letters (wg) in GRAND _ 

 a similar manner in- CHILD *EN F 2 

 dicate recessive char- 

 acters. The children 

 of this cross were hy- 

 brids in ( which the 

 two pairs of charac- 

 ters brought in by 

 the parents (F and 

 wg) were supposed 

 to be mingled as in- 

 dicated in the figure. 

 These children were 

 all smooth and yellow, 

 like one parent, on 

 account of the domi- 

 nance of S and Y 

 over w and g. When 

 close-pollinated or in- 

 bred, these children 

 produced grandchil- 

 dren of four different 

 classes : smooth yel- 

 low ($F), smooth 



green ($#), wrinkled yellow (wF), and wrinkled green (wg). It 

 will be noted that two of these ($F and wg) resemble exactly 

 the original parents, while two {Sg and wY) are new kinds of 

 offspring due apparently to a new combination of the original 



FIG. 99. Diagram illustrating the results derived 



from crossing peas with two pairs of contrasting 



characters 



SY (smooth yellow) are dominant over wg (wrinkled 

 green) . The figure shows the proportionate number of 

 individuals in each class of the grandchildren (F 2 ) and 

 also the composition of each class in terms of SYwg. 



