Varietäten, Desccndenz, Hybriden, 183 



A. A system of partial coupling, under which the gametes con- 

 taining both ot" the factors together are in excess of those containing 

 one or other alone. 



B. A System ot" repulsion , under which it appeared that no 

 gametes carried both of the factors together 1 ). 



Subsequently it was in the Sweet Pea, and later in Primula 

 sinensis, that the oecurrence of coupling or repulsion between the 

 factors in the gametogenesis of the hybrid depends upon the distri- 

 bution of the factors in the original pure parents. Thus, 

 partial coupling oecurs in the heterozygote resulting from the union 

 AB X aD ' b ut Repulsion takes place in the heterozygote resulting 

 from the union Ab X a ^- 



In cases of partial coupling the four kinds of gametes are pro- 

 duced in proportions represented by the general expression 



3n 2 — (2n — 1) : 2n — 1 : 2n — 1 : n* — (2n - 1), 

 where n is one half the total number of gametes. 



Of the Systems thus contemplated, four have been recognized 

 experimentally ; and in all of these cases partial coupling, except 

 one found in Pisum which is as yet untried, repulsion is also pro- 

 ved to oeeur when the first cross is made in the appropriate way. 

 Repulsion has also been found to oeeur in several other cases nota- 

 bly between the factor for femaleness and various other factors in 

 animals. 



Bateson and Punnett discuss the problems encountered in the 

 attempt to form a coneeption of what actually happens in coupling 

 or repulsion, pointing out the difficulty of coneeiving how a system 

 involving 256 terms, such as has been discovered in the Sweet Pea, 

 can be produced in the maturation divisions of the ovarian tissue 

 of such a plant. The heterozygote Ab. aB is ostensibly the same as 

 the heterozygote AB. ab; yet in the one case A and B are repelled, 

 in the other case they are coupled. Since the same factors are in- 

 volved in both cases, it looks possible that the difference in beha- 

 viour may be a consequence of the difference in the geometrical 

 positions of the factors relative to the planes of some critical division 

 in the two cases; there may, in fact, be a difference of polarit}- 

 between the two kinds of heterozygote. 



Systems of three factors. In the Sweet Pea it is known that 

 two distinet factors, viz. erect Standard and long pollen, may be 

 severally coupled with a third factor, that for blue colour. Here, 

 therefore, is a system of inter-relationship between three pairs. A 

 plant heterozygous for B (blue), L (long pollen), and E (erect Stan- 

 dard) can be made by any of four possible unions. Of these that 

 resulting from the cross Ebl X e BL has already been investigated. 

 In it B and E repel, and B is coupled with L. The fact that ß is 

 coupled with L might be expected, but the fact that E is repelled 

 by B rather than by L is worthy of special notice, for we know that 

 E and L repel each other when B is not present. It suggests that 

 there must be an "order of precedence" among the factors compo- 

 sing the system. R. P. Gregory. 



l ) Since these papers were published Punnett has discovered a case of repulsion in 

 which gametes bearing both factors together are formed, but in smaller numbers than 

 those carrying one or other alone. 



