55 



b L X B L = Bald and Lax ( + bearded) 



" X B 1 = Bald and Lax ( + bearded and dense) 



" x b L = Bearded and Lax 



" X b 1 = Bearded and Lax ( + dense) 



b 1 X B L = Bald and Lax ( + bearded and dense) 



" x B 1 = Bald and dense ( + bearded) 



" X b L = Bearded and Lax ( + dense) 



" X b 1 Bearded and dense. 



Without regard to whether the above combinations are constant or in- 

 constant we find 9 which have both of the Dominant characters, viz. : Baldness 

 and Laxness, 3 and 3 with either of the Dominants and either of the Reces- 

 sives and 1 with both Recessives, making in all the 16 combinations indicated. 

 These combinations and proportions may be expressed concisely as follows: 



9BL+3B1+ 3bL+lbl=16. 



These are the normal combinations and proportions which may be ex- 

 pected in an ordinary dihybrid crossing when simple alternating characters 

 are involved. 



That the segregation of the progeny in the second generation of dihybrid 

 crossings actually takes place in the above manner and gives results which 

 correspond very closely with what might be theoretically expected has been 

 shown by numerous investigators working in widely different fields. A good 

 example is afforded by Tedin (72, p. 158) in crossings with pease. In two of 

 the sorts the two dominant characters were red color of flower and black 

 hilum, while the two recessive characters were white flower and light colored 

 hilum. In a third crossing the two dominant characters were yellowness and 

 roundness of seeds, while the recessive characters were greenness and angu- 

 larity of seeds. The characters of the parents together with the actual com- 

 binations and proportions into which the second generation divided them- 

 selves is shown as follows : 



Characters of Parents. 



Dominant Characters Recessive Characters 



Crossing Nos. J" A (Red flowers) a (white flowers) 



I. & II. \ B (Black hilum) b (light hilum) 



Crossing No. JA (Yellow seed) a (green seed) 



III. ^ B (Round seed) b (angular seed) 



