128 THE FIRST PRINCIPLES OF HEREDITY 



recessive characters are indicated by a (green) and h (angular) 

 respectively, then the two pairs of allelomorphs will be Ka 

 and W). The hybrid (F^^) will have the constitution AB«6, 

 but will appear like AB, because A and B are dominant 

 over a and h. 



We can easily find the proportion of the Fg generation. 

 Taking the two pairs of allelomorphs, the offspring will be : 

 three dominant to one recessive for each pair of allelo- 

 morphs — namely (taking sixteen Individuals for Dihybrids), 

 12 A to 4 a and I2 B to 4 h. But now a recombination 

 takes place again in the proportion of three dominant to 

 one recessive. Out of the 12 A, 9 A combine with 9 B 

 (dominant), and 3 A with 3 h (recessive). In the same way, 

 out of the 4 a, 3 « combine with 3 B (dominant), and i a 

 with I h (recessive) , so that we get as result : 9 AB + 3 

 A6 + 3 aB + I ah. How can this result be explained in 

 terms of gametes ? 



As the two pairs of allelomorphs are h.a and B&, and as, 

 according to the law of gametic segregation, only one 

 unit of each pair of allelomorphs can be contained in the 

 same gamete together with any other unit, we get as 

 gametes of the hybrid the following four possible combina- 

 tions : AB, A&, aS>, and db. On further inbreeding of the 

 Fj generation, all the possibilities of the offspring can once 

 more be graphically represented by means of squares, 

 according to Punnett's method, in the following manner : 

 We take this time sixteen female gametes and sixteen male 

 gametes, four each of the above given constitutions, and 

 arrange them, the female gametes vertically and the 

 male horizontally. Then we superimpose the squares, 

 and find thus all the possible combinations of the Fg 

 generation. 



We find as result the following combinations : 



I. I ABAB^ II. I khh})\ 



2 ABAb I .-D 1 Khah ] '^ ^^ ' • -.w v. u 



A-D TD r^AB.. IV. \ ahah. 



2 ABaB III. I aBflB ^ ^g 



4 ABflfe J 2 dQah 



