HEREDITY IN PLANTS, ANIMALS, AND MAN. 369 
surprise you. Albino-eyed female mated with pure red-eyed male gave 
6 red-eyed and 3 black-eyed young. Albino-eyed female mated with 
hybrid black gave in four broods 75 black-eyed and 15 red-eyed young.* 
In the grandchildren from both crosses, however, you will see that the 
albino-eyed form reappears. 
From this it follows :— 
(1) that the factor for albino eye is transmitted from parent to off- 
spring, but that colour is dominant and albino recessive, for when 
albino is mated with coloured eye no albinos occur in the first 
generation of offspring ; 
(2) that the original albino-eyed female must have contained the factor 
tor black, since black offspring were produced when it was mated 
with pure red, which we know from the previous work contains no 
black ; 
(3) that the albino-eyed female must contain the factor for red, and 
this for two reasons: in the first place, if it had contained black 
only we should have got only black offspring when it was mated 
with red, for we know that black is dominant to red ; in the second 
place, and again because black is dominant to red, if the albino 
had contained black only, when mated with the black hybrid we 
should have had only black offspring, whereas we obtained 75 black- 
eyed and 15 red-eyed. We know that when the hybrid, containing 
red and black, is mated with another hybrid of the same kind 
the resulting offspring should be 3 black to | red. 
We must now look more closely at the grandchildren of the original 
albino-eyed female, which were all obtained by mating together her im- 
mediate ofispring of the F.1 generation. When two blacks were mated 
together in F.1 two kinds of broods resulted, some in which only black 
and albino-eyed young occurred, others in which black, red, and albino 
were present. When two F.1 reds were mated together the broods con- 
tained red-eyed and albino-eyed young. (See Diagram 7.) 
This resembles closely what is found in coat colour in animals such as 
rabbits, mice, and rats, which has been worked out by Bateson, Punnett, 
and others. To explain the phenomena these authors assume that in 
order that the colour in the coat of an animal may be visible it is necessary 
that at least two factors should be present, one factor representing the 
colour itself —say black or brown, as the case may be—and a second 
factor which must be present in order that the colour may show itself. 
In the absence of this latter factor, which they call the colour factor, the 
* In the diagram one brood only is shown from this mating, consisting of 7 black-eyed 
and 2 red-eyed young, 
NEW SERIES.—VOL. XI. NO. 8. DECEMBER, 1917, 2B 
