126 THE FIRST PRINCIPLES OF HEREDITY 



Gametes 



F, 



Gametes 



dominants as DD, the impure dominants as DR, and the 

 extracted recessives as RR.) We can now enlarge dia- 

 gram Fig. 49 by showing the gametes of the different 

 generations and their union. We have the dominant and 



recessive parent D and 

 R, which produce by 

 the union of their 

 gametes d and r the 

 hybrid D(R). This 

 hybrid has an equal 

 number of gametes d 

 and gametes r, which, 

 as indicated in the 

 diagram by the arrows, 

 produce one pure domi- 

 nant, one pure reces- 

 sive, and two impure 

 dominants. 



This theory of the 

 segregation of the unit- 

 characters can be 

 tested by further ex- 

 periments, and results 

 have been attained 

 verifying with mar- 

 vellous correctness the 

 supposition made. Assuming that the gametes of the ex- 

 tracted dominant DD contain the character d only, those 

 of the extracted recessives RR the character r, while the 

 gametes of the impure dominants DR contain in equal 

 numbers the character d or character r, then, if crossing 

 takes place, the following will be the result : 



DDxRR=all DR, as aU gametes d unite each with 

 a gamete r, thus giving DR. 



DR X RR= I DR -f- 1 RR, for we have half the number 

 of gametes of DR containing d, half the number 



DD 



Fig. 



D(R) D(R) 



51. — Gametic Segregation. 

 (After Thomson.) 



