Mutations and Evolution . 
67 
Duplicate Factor Mutations. 
This fact is thus emphasized because later generations produced 
some families with 15 :1 ratios, hence representing two factors for 
red, in addition to families with 3 : l. 1 Furthermore, certain 15 : 1 
families came from members of families showing a 3: 1 ratio. 8 
These must therefore have been due to secondary mutations. The 
evidence, part of which has been considered elsewhere, 8 shows with 
a high degree of probability that, as we have seen, the original 
mutant was heterozygous for a single factor for red. Shull (1914a), 
unfortunately, from a study of hybrids between rubricalyx and 
(E. grandiflora which he mistook for pure rubricalyx , drew erroneous 
conclusions regarding the origin and behaviour of this striking form. 
Another important feature in its history, already mentioned, is the 
fact that members of a family of rubricalyx which contains a single 
factor for red, as shown by the 3 :1 ratio, can give rise to individuals 
which are heterozygous for two factors for red. How this may 
come about has been discussed under the name duplicate 
mutation 4 . 
That two or even three factors for the same character may 
exist in a given strain, was first shown by Nilsson-Ehle (1909) for 
wheat, and has since been demonstrated in a number of other 
forms. Nilsson-Ehle showed for example that while Extra 
Squarehead wheat has only one factor for red kernels, Sammet and 
Grenadier have three, and in a later paper (1911) that Swedish 
Binkel has two. A list of such duplicate determiners has been 
given by Shull (1914b). It includes glume colour, hairiness of glumes, 
length of glumes, width of leaves, etc., in oats, and various 
characters in beet, turnip, gourd, flax, tobacco, bean, pea, velvet 
bean, wheat, and maize among plants; also body weight in ducks, 
fecundity in fowls, skin colour in man, ear length and body size in 
rabbits, piebald coat colour in mice and the hooded pattern in rats. 
Of course some of these cases are much better substantiated than 
others, and the number of cases has since been considerably 
increased. The Howards (1912) have demonstrated one of the 
clearest cases of duplicate factors for red in wheat. 
Nilsson-Ehle did not consider the origin of this condition of 
duplicate factors in wheat, but it appears probable that it has the 
1 Gates 1915b» 
3 Some 5 : 1 ratios were also obtained, which are probably to be explained 
by linkage. 
8 Gates 1915e, 
4 Gates 1915b. 
