Xo..V)0] 



GAMETIC COUPLING 



57.-, 



Returning to the consideration of the original example 

 of gametic coupling in the sweet peas, the coefficient of 

 association, .958 ± .004, is seen to be intermediate be- 

 tween that resulting from a 7 : 1 and an 8 : 1 ratio. 



Notwithstanding the fact that the figures correspond 

 somewhat more closely with an S : 1 than they do with a 

 7:1 ratio, an evident preference for numbers that arc 

 powers of 2 is shown when the possibility of an 8:1 ratio 

 is discussed. Instead of saying that IS gametes are con- 

 cerned, the number is spoken of as l() + 2, and the fact 

 that a ratio of to: i> would give almost exactly the oh 



The next example of gametic coupling to he reported 

 was in the same series of crosses ( liateson, Saunders 

 and Punnett, 1908, p. 11), where the progeny of four 

 individuals showed the following grouping: 29(> : 19 : 1*7 : 

 85. This is referred by the authors to the theoretical 7 : 

 1 ratio, though it shows almost the same association as 

 an 8:1 ratio, that is, .960. The probable error, .008, 

 would indicate, however, that with this number of indi- 

 viduals such a deviation might easily be due to chance. 

 The numbers are, therefore, too -mall to afford evidence 

 affecting the choice between a 7 : 1 and an 8 : 1 formula. 



From the progeny of one of these four individuals 

 c<tnsi<ting of 111 plants and showing an association of 

 .914, 10 individuals showing both dominant characters 

 were selected and propagated. The progeny of the 10 

 plants taken together gave the following grouping 49:: : 

 25:25:138. This grouping is considered only in con- 

 nection with the 7:1 and 15:1 distribution, though the 

 association .982 ±.004 would indicate that a gametic 

 series of 12: 1 would most closely fit the numbers. The 

 deviation from the 7:1 ratio is 9 times the probable 



With respect to the characters considered separately, 

 the classes secured from each of the 10 individuals 

 showed a remarkable conformity to the expected 3:1 



