108 Mr. G. P. Mudge. On the Hereditary [May 8, 
Hxpervment 64. 
In this experiment the albino was extracted from a cross of Cr 6 bx Cr 6 6 
(experiment 50). Reference to the table of gametic combinations on p. 103 will 
show that an albino thus extracted may be either ceBsP, egBSP, or cgBSsP. 
If it be egBSP, then a Cr 6 a is expected in its offspring when crossed with 
a Or 6 6; if it be cgBSsP, then a Cr 5 is additionally expected. 
Assuming it to be egBSsP, the full expectation is 
A Cra Cr 5- i) Cr o-22 Gr 60) 
The actual result of this mating in two litters is 3 Crd+2 Cr6a+8 Cr60. 
The expected albinoes are therefore missing, and there is a preponderance of 
the Cr 66 type. But since the Cr 5 and Cr 6a types were both absent in the 
first litter, it is possible that the expected Cr 4 types would have appeared 
had the parents hved to produce a third litter. 
The appearance, however, of the Cr 6 a type among the offspring can only 
occur if the parental albino is carrying the self-pattern determiner, and the 
presence of the Cr 5 type can only occur if it carries an allelomorph, 2.2. , 
which, being recessive to it, will therefore allow P to be manifested. 
The presence of Cr 6 a together with that of the Cr5 type, must therefore 
be regarded as initial evidence that this type of albino has been actually 
produced. And, since it is predicted (see table of gametic combinations, 
p. 103) that some of the albinoes produced in a cross of Cr6 6x Cr6 6 will be 
of the two types cgBSP and cgBSsP, it thus far constitutes a fulfilment of 
the prediction of the existence of this latter type in contrast to the former. 
(4) “Lrish” bx Grey with White = Cr 6 bx Cr 2. 
One cross only (experiment 66a) of this nature has been made, but the 
result is of exceptional interest, and affords a cogent test of the doctrine of 
gametic purity and of dominance. 
To understand the case, it is necessary to consider the origin of the Cr2 
member of the pair. Its parents were a black variety of the wild grey rat 
(experiment 48) x with an albino purchased of ordinary dealers. In this 
mating there were seven young, six being of the expected “Irish” 6 type and 
one exceptional one, @.¢., a Cr 2. In my other crosses of this nature there 
were 13 young, all of the “ Irish” 6 type. 
To explain the production of this Cr 2, it is necessary to assume that the 
albino rat which was mated to the black variety of grey was carrying the 
erey determiner.* For reasons which will appear later, I will further 
* The same result would be obtained by supposing that the black variety of wild grey 
was carrying the grey chromogen. But since grey is dominant to black this cannot ) - 
the case. 
