66 
Notes on Recent Literature. 
was obtained in the Sweet Pea, in which it is quite clear that 
repulsion is partial also ; that is to say, all four kinds of gametes 
are formed by the hybrid, but those bearing one or other factor 
alone are produced in greater numbers than those kinds containing 
respectively both factors or neither factor. The characters with 
which we are concerned in this case 1 are normal flowers (N) and 
fertile anthers (F), as contrasted with a peculiar malformation of 
the flower (“ Cretin ”) (n) and sterile anthers (f). A Cretin fertile 
was crossed with various normal steriles. The F 2 ’s from these 
crosses gave results which clearly show that the series of gametes 
produced by the heterozygote is INF : 3Nf : 3nF : Inf. Such 
a series of ovules fertilized by a similar series of pollen grains 
would give 33 normal fertiles, 15 normal steriles, 15 cretin fertiles 
and 1 cretin sterile; the actual numbers obtained are 336 normal 
fertiles, 150 normal sterile, 143 cretin fertiles, 11 cretin steriles. 
It will be noticed that when partial repulsion is of even such 
a low form as 1 : 3 : 3 : 1, only one double recessive, aabb, is to 
be expected in every 64 F 2 -plants; as repulsion increases in 
intensity, zygotes of this form will become scarcer and scarcer, 
until under repulsion of the form corresponding to the highest form 
of coupling yet recognized, namely 1 : 127 : 127 : 1, only one such 
individual in every 65,536 F 2 -individuals is to be expected; at the 
same time the zygotic types encountered in the F 2 approach more 
and more nearly to the ratio 2AB : lAb : laB, which would be 
given by complete repulsion. This being so, the principle of partial 
repulsion, discovered in the case just described, may almost certainly 
be extended to all cases of repulsion in plants and probably in 
animals also 3 ; and at the same time the occasional occurrence of 
aabb-types in F 3 ’s exhibiting repulsion, which was mentioned above, 
receives an explanation. 
It therefore appears that the double heterozygote AaBb, may 
produce the four kinds of gametes in any one of the numerical 
ratios represented by the general expressions 
AB Ab aB ab 
( n —1) : 1 : 1 : (n—1), 
1 : 1 : 1 : 1 , 
1 : (n—1) : (n—) : 1. 
It is difficult to resist a speculation as to whether the ratios 
are always such that the smaller terms are to be represented by 
unity, or whether ratios may not occur of the form (n—x) : x : x : 
(n—x) where x is any odd number less than n. As yet, however, 
no instances of ratios with x > 1 have been identified ; in one 
or two cases, it is true, the constitution of the F 2 ’s, as judged 
from the visible characters of the plants, is rather suggestive of a 
partial coupling or repulsion of a lower order than 3 : l 3 ; but, for 
1 Sec Bateson & Punnett. Journ. Genetics, I, p. 294, 1911. 
2 Bateson & Punnett do not commit themselves as regards the 
application to cases of repulsion in animals, see l.c. p. 301. 
3 See, for instance, Gregory, Journ. Genetics, 1, pp. 125—129, 
1911. The possibility there suggested, that the numbers 
observed in certain F 2 ’s might be explained if partial coupling 
were found to take place in the gametes of one sex only, has 
been negatived by subsequent experiments, which have 
shewn that both ovules and pollen grains form coupled 
series (see Roy. Soc. Proc. B, 84, p. 14, Table II). 
