520 



EVOLUTION, HEREDITY, EUGENICS 



and yields the i : 2 : i offspring if two are hybridized. When the 

 recessive is crossed with a mixed DR we get 2 D (R) plus 2 RR. 



Mendelian Inheritance 

 (Garden Peas) 



Dominant 

 R. round 

 Y. yellow 

 T. tall 



Recessive 



W. wrinkled 

 G. green 

 D. dwarf 



Pure dominant crossed with pure recessive yields DR hybrids. 



Monohybrids.—R X W equals first filial generation: R (W). 



Representing the hybridization as followed by crosses of male 

 and female germ cells bearing the combined R (W) we have by 

 Punnett's method of squares the following Monohybrids: 



F2 generation 



This equals RR plus 2 R (W) plus WW. 

 Likewise DR X DD is expressed: 



R R 



X = 2 RR plus 2 RW. 

 R W 



Again, dominant-recessive DR X pure-recessive RR equals 2 DR 

 plus 2 RR as: 



R W 



X =2 RW plus 2 WW. 



w w 



Complete dominance is rare, however, as Mendel discovered in the 

 case of certain peculiar hybrid forms. 



{a) The law of dominance is not of universal application. 

 Mendel found this true in crossing different heights of peas. 



{b) There may be an intensification of the characters of one 

 parent. Brown seeded peas may be darker than the parents. 



