b 
d 
: 
1907.| Transmission of certain Coat Characters in Rats. 109 
assume that the albino also carried the black and piebald pattern determiners. 
Its composition will then be represented by cGgBsP. Such an albino, mated 
with a homozygote black, will produce, according to the subjoined Table II, 
equal numbers of “ Irish” 6 and Cr 2. 
Table I].—Predicted Offspring in a Cross of Cr 7 (extracted) xCr 4 
(extracted). The albino is carrying the grey determiner and may be 
either cGgBsP or cGgBSsP. 
Gametes formed by | Gametes formed by Zygotic composition ie uy 2y aa 
self black. albino. of the offspring. pide insite lec 
| offspring. 
CgBSP x cgBsP = CegBSsP = Cr 6 
CgBSP x cGBsP = CcGgBSsP = Cr 2 
CeBSP % _cGBSP = CeGgBSP = Cr 2 
CgBSP * egBSP = CcgBSP = Cr 6a 
Total Offspring. 
If albino = cGgBsP = 1Cr2+1(Cr6 4. 
ie = cGgBSsP = 2 Cr2+1Cr66+1Cr6a. 
If the assumption that the albino parent is carrying the grey determiner 
be correct, then the exceptional Cr 2 member among the offspring, in 
experiment 48, may be assumed to be of the zygotic composition CeGgBSsP. 
If we ascertain the possible gametic combinations when such a Cr 2 indi- 
vidual is crossed with an “Irish” 4 of CegBSsP composition, it will be such 
that the F 1 offspring predicted will be as follows :— 
Se@m4 ede Or b-28 Cr 24 3.Cr3+3 Cr5+2 Cr 6a+6 Cr 6641 Cr 7 
= 1 Cr 4:3 pigmented. 
Now, the special feature in this progeny is the presence of the black forms, 
especially the homozygote Cr 7. Grey being dominant to black, black 
individuals could not appear in the F 1 generation of a cross between 
grey (Cr 2) and black (“Irish” 6), unless the grey member carried black 
recessive. 
Therefore, if black members of any coat pattern actually appeared in the 
F 1 generation of this cross of “Irish” 6 x Cr 2, it must be accepted as 
evidence that the Cr 2 carried black recessive. And, since on no other 
hypothesis, as far as I can see, could these black members appear—bearing in 
mind the unquestioned dominance of grey—unless gametic purity or segrega- 
tion of unit characters really occurs, it must also be accepted as a cogent 
proof of the truth of this doctrine. 
